Particulate medium prepared from partially decomposed organic matter for selective sorption between competing metal ions in aqueous solutions

ABSTRACT

A process for the preparation of a granulated or pelletized sorption medium from a partially decomposed organic material like peat, followed by low-temperature thermal activation of the sorption medium to produce a high degree of granule or pellet hardness balanced against an efficacious level of ion-exchange and adsorption capacity, followed by chemical treatment of the sorption material via a preselected solution of soluble salts (called “APTsorb II*M”) for use in a wastewater treatment process where competing toxic metal cations are present in the wastewater is provided by this invention. Depending upon the M+ cations contributed to the peat granule sorption activity sites by the preselected salt used in the salt solution treatment step, the granules exhibit a selectivity α of a first type of more-toxic metal cations (such as cadmium, lead, copper, or other metals at high concentrations) over a second type of less-toxic metal cations of (such as zinc, aluminum, or iron) in the wastewater; greater adsorption activity for the first type of more-toxic metal cations; and greater breakthrough capacity for the first type of more-toxic metal cations. This allows the end user to target the more-toxic metals for adsorption by the sorption medium containing the cations contributed by the preselected solution of soluble salts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 14/213,677 filed on Mar. 14, 2014, which is a continuation-in-part of U.S. Ser. No. 13/841,526 filed on Mar. 15, 2013 both entitled “Particulate Sorption Medium Prepared from Partially Decomposed Organic Matter,” which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates generally to particulate sorption media prepared from partially decomposed organic matter like peat, and more specifically to granules made from such material that are thermally activated and chemically modified to provide them the requisite hardness and sorption capacity for selective sorption of competing metal ions found in aqueous solutions like waste or mine waters.

BACKGROUND OF THE INVENTION

Many industrial manufacturers face the problem of wastewaters containing heavy metals like arsenic, lead, mercury, cadmium, iron, and aluminum that are produced by their manufacturing process. Circuit board manufacturers, metal finishers, automotive, aerospace, and semiconductor manufacturing, electroplated metal parts/washing, textile dyes, and steel are prime contributors. If dissolved in heavy-enough concentrations in the wastewater stream, they become toxic when they are not metabolized by the body, and accumulate instead in the soft tissues. Heavy metal toxicity can result in damaged or reduced mental and central nervous function, learning disabilities, diminished energy levels, cancers, damage to blood composition, lungs, kidneys, liver, and other vital organs, and even death. Other heavy metals of concern found in wastewater streams include antimony, chromium, cobalt, copper, manganese, nickel, uranium, vanadium, and zinc.

It is therefore necessary for manufacturers to treat these industrial wastewater streams to reduce these heavy metals to acceptable levels before they are introduced into water streams and water bodies that are subject to environmental government laws and regulations. As a result of improper treatment prior to discharge, many heavy metals have been found to exist at harmful levels in ground waters which are destined for potable drinking water. Agricultural, meat packing, mining, and hydrofracking industries also face particular risks of waste water contamination.

A “solution” represents a mixture of two or more individual substances that cannot be separated by a mechanical means, such as filtration. For example, a liquid solution occurs when a liquid, solid, or gas solute is dissolved in a liquid solvent. The liquid solution constitutes an aqueous solution if the solvent is water. Wastewater streams very often constitute aqueous solutions containing one or more contaminants.

Chemical Water Treatment Methods

Chemical treatment methods are known in the industry for processing wastewater streams. In one commonly used method, the wastewater is treated with a caustic agent like hydroxide to adjust the pH of the water so that the metals contained therein form insoluble precipitates. A coagulant in the form of an organic ferric chloride or ferrous sulfate is then added to the water to promote settling of the metal hydroxide precipitates. The precipitate particles settle into sedimentation tanks. A filtration medium like silica sand, diatomaceous earth, carbon, or cloth is then used to capture the remaining metal hydroxide found in the water. But, this process requires very large volumes of chemicals, as well as land-filling or treatment of the resulting toxic metal sludges.

Non-Chemical Water Treatment Methods

Non-chemical treatments of wastewater generally employ a mechanism known as “sorption.” Sorption can involve both chemical and physical processes, but the end result is the transfer of a substance from one phase to another. In other words, sorption is the movement of toxins and contaminants from the dissolved, aqueous phase to the surface of a solid media. Three different types of sorption predominate wastewater treatment technology: ion-exchange, absorption, and adsorption.

Ion exchange is a separation process widely used in the food and beverage, hydrometallurgical, metals finishing, chemical and petrochemical, pharmaceutical, sugar and sweetness, ground and potable water, nuclear, softening and industrial water, semiconductors, power, and many other industries. Aqueous and other ion-containing solutions can be purified, separated, and decontaminated by swapping targeted ions contained in the solution with substitute ions typically provided by ion exchange resins or other substrates.

But ion exchange is also a proven technology for removing dissolved metals or other impurities from these wastewater streams. It represents a reversible process in which the ionized metal or other impurity compound or element changes place with another ionized compound or element on the surface of a medium like an ion exchange resin.

Ion exchange can produce high-purity water (including softening, deionizing, water recycling, and removal of heavy metals) from the wastewater. In a familiar example to many readers, an ion exchange-based water softener works by passing hard water naturally containing an abundance of calcium and magnesium cations through a volume of resin beads containing sodium ions on their active sites. During contact, the calcium and magnesium cations will preferentially migrate out of solution to the active sites on the resin, being replaced in solution by the available sodium ions. This process reaches equilibrium with a much lower concentration of calcium and magnesium cations in solution, thereby “softening” the water. The resin can be recharged periodically by washing it with a solution containing a high concentration of sodium ions, such as a sodium chloride solution. The calcium and magnesium cations accumulated on the resin will migrate off it, being replaced by the sodium ions from the salt solution until a new equilibrium state is reached.

Synthetic ion exchange resins are typically used within ion exchange processes. These synthetic resins commonly are formed of small 0.03-2.0 mm beads made from an organic polymer substrate, such as cross-linked styrene and divinylbenzene copolymers. Moreover, these resin beads will feature a highly developed structure of pores on the surface of the resin, which provide the sites for trapping and releasing ions. These resin beads can be converted to cation-exchange resins through sulfonation, or to anion-exchange resins through chloromethylation.

In wastewater treatment, these ion exchange resins remove the heavy metals from the solution, and replace them with less harmful elements like potassium or sodium. But, this process for producing synthetic resins is expensive. The resin beads are also highly susceptible to “fouling.” While soluble organic acids and bases removed by the synthetic ion-exchange resin are shed during regeneration, non-ionic organic materials, oils, greases, and suspended solids also removed from the water tend to remain on the surface of the resin bead. Foulants can form rapidly on the resin, and can significantly hinder performance of the ion-exchange system. Cationic polymers and other high molecular weight cationic organics are particularly troublesome at any concentration. For certain types of resins, even one ppm suspended solids can cause significant fouling of the resin beads over time. Thus, a prefiltration unit in the form of activated carbon or other separation material may need to be positioned upstream of the ion-exchange unit to remove these organic contaminants before the wastewater is passed through the ion exchange resin, further complicating the water treatment process and its costs. The costs associated with this pretreatment can be substantial.

Additionally, resins require regeneration once the ion-exchange sites have been exhausted, for example, as feedwater flows through a bed. During regeneration of a cationic resin, metal cations that were previously adsorbed from the wastewater flow, are replaced on the resin beads by hydrogen ions. A step known as “backwash” is often employed during regeneration, so that any organic contaminant buildup in the resin can be relieved, thereby allowing free flow of the wastewater through the resin beads. But, chemically-regenerated ion-exchange processes known in the art tend to use excessive amounts of regeneration chemicals, which require periodic and even on-going treatment, as well as safe disposal of the chemical waste. These processes can be complex and expensive to operate.

Another “sorption” separation process is absorption. This is a physical or chemical phenomenon or process in which atoms, molecules, or ions enter some bulk phase, whether it be a gas, liquid, or solid material. The gas, liquid or solid material takes in the other substance, like a sponge soaking in water. But absorption is necessarily limited by the physical capacity of the absorbent substrate, and can require frequent purges of the taken-up substance to replenish the absorbent capacity of the substrate.

Yet another sorption process is adsorption. This represents a process in which atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to the surface of a substrate. This constitutes a surface-based separation process, instead of absorption which involves the whole volume of the substrate material. Like ion exchange, certain adsorbates in the adsorption process are selectively transferred from the fluid phase to the surface of insoluble, rigid particles.

Activation of Carbon-Based Media

“Activation” is the process of treating a material that is high in carbon for purposes of increasing surface area and creating porosity. Materials can be activated either with chemical treatment followed by a thermal step, or with heat treatment alone. Most commonly, carbon materials that have been activated then undergo further chemical treatment in order to change the activity of the surface of the carbon-based material.

Activated carbon substrates have been employed in the water filtration industry for this adsorption separation process. Unlike synthetic polymer resins used in ion exchange processes, these activated carbon materials constitute a form of carbon that has been processed to make it extremely porous with a resulting very large surface area for adsorption of impurities via van der Waals forces or London dispersion forces, or chemical reactions. Due to its high degree of microporosity, just one gram of activated carbon substrate can provide a surface area exceeding 500 m² (about one tenth the size of a football field). Moreover, such activated carbonaceous materials can be produced from a variety of natural organic materials like vegetable matter, soft woods, cornstalks, bagasse, nut hulls and shells, various animal products, lignite, bituminous, or anthracite coals, straw, petroleum pitch, or peat.

Chemical Activation

When some of the energy required for a reaction is provided by a preceding exothermic chemical reaction, there is said to be a “chemical activation.” Carbonaceous material may be chemically activated by impregnating it with an acid, strong base or a salt like phosphoric acid, sulfuric acid, potassium hydroxide, sodium hydroxide, calcium chloride, or zinc chloride, followed by carbonization via pyrolysis at a high 450-900° C. temperature range. For example peat can be impregnated with phosphoric acid or zinc chloride mixed into a paste, and then pyrolyzed at 500-800° C. to activate the peat, followed by washing, drying, and grinding this chemically activated peat into a powder to produce activated carbon having a very open porous structure that is ideal for adsorption of large molecules.

For example, Soviet Published Patent Application No. 1,142,160 filed by Sokolov et al. discloses an active adsorbent product made from aluminum salt sludge. Organo-aluminum sludge produced in the process of coagulation of aluminum salts in water is thickened to create a concentration of 10-17%. The aluminum hydroxide fraction is used to precipitate out the organic compounds during a process that is called coagulation. The aluminum hydroxide and organic compounds are then treated with sulfuric acid, and then the solid phase is heated at 210-270° C. for 2-4 minutes. This process destroys the organic material to convert it into activated carbon, and some portion of organic material is reacted with sulfuric acid to produce sulfonic acid derivatives. The end product is used to remove organic compounds and metal cations (e.g., nickel and cobalt) from waste water. But, not only does Sokolov use a non-natural starting material, but also he relies upon a combination of chemical activation to produce activated carbon, and chemical modification to produce the SO₃ ⁻ groups on the surface of the product necessary for yielding its cation-exchange properties.

Physical Activation

Alternatively, carbonaceous materials such as coconut hulls or bamboo can be physically activated by exposing the material to an oxidizing atmosphere like carbon dioxide, oxygen, or steam at a very high temperature falling within the 650-1200° C. range. These processes for producing activated carbon do not produce a media with a usable ion-exchange capacity. As an example, U.S. Pat. No. 6,316,378 issued to Giebelhausen et al. discloses the manufacture of shaped activated carbon pellets. Polymer resin, acetylene coke, or pearl cellulose are dried at 250-300° C. Then Giebelhausen carbonizes his material at a very high 850-880° C. temperature without steam. Finally, he thermally activates his carbon pellet product at an even higher 910-915° C. temperature in a hot gas-fired kiln. Steam is used by Giebelhausen merely to prevent explosions.

In another example, U.S. Published Application 2003/0041734 filed by Funke et al. shows a method for producing an ultra-low emission (“ULE”) carbon material. The Funke reference explains that conventional activated carbon materials contain too much water and carbon dioxide constituents to effectively adsorb water and carbon dioxide molecules from a gas stream in need of purification. Therefore, Funke subjects activated carbon with no ion exchange capacity to extremely high temperatures and time in a reactor in order to drive off all the H₂O and CO₂ molecules from the activated carbon. This “preconditioned” ULE carbon material is then further treated to a second activation process under the flow of an ultra-dried reactive purge gas like ammonia to remove any additional moisture from the ULE carbon material. Devoid of H₂O and CO₂ molecules, this processed carbon material can readily adsorb new H₂O and CO₂ molecules from the gas stream by simple adsorption without any ion exchange reaction. Furthermore, such treatment conditions are on the order of 500-700° C. for 24 hours to 5 days. Indeed, these are extreme conditions that in no way resemble normal physical activation.

Pyrolysis of Peat

“Pyrolysis” is related to activation in that material high in carbon content is exposed to heat. Activation often involves pyrolysis, but the end result is to produce a product with increased surface area. Pyrolysis constitutes the decomposition of organic material through heating, and it occurs in an oxygen-free environment.

Peat is a substance that can be pyrolyzed, and comparative studies of the pyrolysis kinetics for coal and peat have been performed. See Durusoy et al., “Pyrolysis Kinetics of Blends of Gediz Lignite with Denizli Peat,” Energy Sources, vol. 23, pp. 393-99 (2001). But, no particular temperature ranges for pyrolysis were determined in this study, nor was any ion-exchange medium prepared.

Common Uses of Activated Carbon

Activated carbon filters are popular for home and small-volume water purification systems, because of the adsorbency of the carbon substance. Activated carbons are known to have a heterogeneous pore structure, which is classified as microporous (diameter of pore <2 nm), mesoporous (diameter of pore between 2-50 nm), and macroporous (diameter of pores >100 nm). Activated carbons have a large adsorption capacity, preferably for small molecules, and are used for purification of liquids and gases. Volatile organic chemicals found in the water are removed via adsorption. But, activated carbon filters are generally not successful in removing dissolved metals like antimony, arsenic, barium, beryllium, cadmium, chromium, copper, mercury, nickel, and selenium from the water. Moreover, the purification efficiency of activated carbon filters is directly influenced by the amount of carbon contained in the filter unit, the amount of time that the water-borne contaminant spends in contact with the carbon, and the contaminant particle size. Hence, activated carbon filters must necessarily contain very large carbon volumes treating very low water flow rates, which makes them comparatively unsuitable for processing industrial wastewater streams.

Peat-Based Sorption Media

It would therefore be desirable to produce a sorption medium from a natural, organic material. However, a balance must be struck between the physical integrity of the form of the sorption medium versus the ability of the medium to serve as an ion-exchanger, adsorbent, or absorbent. Partially decomposed organic starting material like peat inherently possesses ion-exchange and adsorbent characteristics. Peat is composed mainly of marshland vegetation, trees, grasses, fungi, as well as other types of residual organic material such as insects and animal remains, and is inhibited from decaying fully by acidic and anaerobic conditions. It is also abundant in many places in the world. For example, 15% of Minnesota is covered by valuable peat resources, comprising 35% of the total peat deposits found in the lower 48 states in the U.S.

Pellets made from peat are known within the industry. For example, U.S. Pat. No. 6,455,149 issued to Hagen et al. discloses a process for producing peat pellets from an admixture of peat moss, pH adjusting agent, wetting agent, and other processing additives. The resulting granules can be easily broadcast spread on the ground, and returned to their original peat moss form upon wetting to act as a fertilizer. No effort is made, however, by Hagen to activate his pellets to prepare the adsorption or absorption or ion exchange characteristics of their surface, nor are they used as an ion exchange medium. U.S. Pat. No. 3,307,934 issued to Palmer, et al. shows another fertilizer product containing peat, and water-soluble inorganic fertilizer salt like diammonium phosphate, sulfate of potash, or urea. This peat product likewise is not activated, nor is it used as an ion-exchange or adsorption medium. Instead, Palmer uses peat merely as a carrier for his fertilizer salt.

It is also known in the wastewater treatment industry to use pellets made from other natural organic materials besides peat as a pollution filtering medium. For instance, U.S. Pat. No. 5,624,576 issued to Lenhart et al. illustrates pellets made from leaf compost, which are then employed to remove pollutants from storm water. U.S. Pat. No. 6,143,692 issued to Sanjay et al. discloses an adsorbent made from cross-linked solubilized humic acid, which can be employed for removing heavy metals from water solutions. U.S. Pat. No. 6,998,038 issued to Howard contains a detailed disclosure of a storm water treatment system for which the filtering media can include peat. U.S. Pat. No. 6,287,496 issued to Lownds shows a process for preparing peat granules using a binder and gentle extrusion. In U.S. Pat. No. 5,578,547 issued to Summers, Jr. et al., a mixer machine and process for producing peat beads for adsorption of metal cations at dilute concentrations (<10 ppm) is disclosed. Peat and a sodium silicate or polysulfone/methylene chloride binder are fed to the mixer to form a pellet, followed by drying. This binder chemical acts like a glue to fuse the peat fibers together in order to create a stronger peat pellet. But, Summers and others fail to disclose or suggest any thermal activation process step, nor to demonstrate the selective removal of cadmium ions from wastewaters in the presence of high concentrations of zinc ions. See also U.S. Pat. No. 5,602,071 issued to Summers, Jr. et al.

Russian Patent No. 2,116,128 issued to Valeriy Ivanovych Ostretsov teaches a process for producing a peat sorbent useful for removing oil spills from solid and water surfaces. The peat material is dried from 60% moisture to 23-25% moisture, and then compressed at 14-15 MPa pressure into briquettes. Next, these peat briquettes are heated at 250-280° C. without the use of additional hydrophobic chemicals and without air. The humic and bitumen fractions within the peat mobilize to the surface of the peat briquettes to produce a natural hydrophobic coating. This hydrophobic coating is necessary for the peat briquettes to be able to soak up oil. Ostretsov also reduces the moisture of his heat-treated peat briquettes all the way down to 2.5-10% wt. moisture. This significant water reduction assists with the hydrophobic coating formation and frees up the pores in the peat material so that they are available to soak up oil. Unfortunately, Ostretsov's aggressive thermal treatment of his peat material will reduce hardness, but he does not need to worry about hardness in his peat briquettes, because he does not force water through the briquettes under pressure during waste water treatment. Instead, he merely floats his peat briquettes on the water surface to soak up the oil spill. Indeed, this is not an ion-exchange medium.

Russian Patent No. 2,173,578 also issued to Ostretsov discloses a similar peat sorbent product useful for soaking up oil spills on water surfaces. His peat under this patent disclosure is milled at low decomposition and dried to 20-48% moisture, and then compressed under pressure at a force below 10 MPa, and then heated under a carbon dioxide blanket without oxygen for 20-90 minutes “at a temperature of 15-30° C. above the exuding temperature of water-insoluble resins of the carrier.” However, it is clear that Ostretsov's process will produce a hydrophobic coating on the surface of his peat material, which is the opposite of the hydrophilic surface that is required for adsorption of metal cations from wastewater streams.

Peat is a substance that can be pyrolyzed, and comparative studies of the pyrolysis kinetics for coal and peat have been performed. See Durusoy et al., “Pyrolysis Kinetics of Blends of Gediz Lignite with Denizli Peat,” Energy Sources, vol. 23, pp. 393-99 (2001). But, no particular temperature ranges for pyrolysis were determined in this study, nor was any ion-exchange medium prepared.

Peat as an Ion-Exchange Media

Various efforts have been made to prepare ion-exchange mediums from peat starting material which is chemically activated and, in some cases, chemically modified before the chemical activation step. For instance, U.S. Pat. No. 4,778,602 issued to Allen, III teaches a multi-functional filtering medium consisting of highly humified peat which is treated with an alkaline solution to hydrolyze the humic and fulvic acid fractions contained therein. Next, the peat product is treated with a quaternary amine solution to precipitate out the humic and fulvic acid fractions from the peat. After filtering the drying the peat cake, nitric acid or sulfuric acid is added to neutralize the amine to chemically modify the peat to increase its cation exchange sites by either adding SO₃ ⁻ groups to the peat surface structure, or to oxidize the organic carbon to improve the cation exchange capacity. Finally, the peat residue may be treated to a semi-coking process step at 200-1000° C. at a 40 psi pressure, thereby allowing carbonization of peat residue. This will actually destroy the carbon fibers. Thus, Allen actually chemically modifies his peat product to increase the cation exchange sites, followed by chemically activating it to increase hydrophobic adsorption properties. The enhanced cation exchange capacity is also aided by destruction of the carbon fibers via the semi-coking (pyrolyzation) step.

U.S. Pat. No. 6,042,743 issued to Clemenson discloses a method for processing peat for use in contaminated water treatment. Clemenson mixes raw peat with heated sulphuric acid to produce sulfonated peat slurry. After cooling and drying the slurry admixture to a 60-70% moisture content, he adds a binder like bentonite clay to coagulate the acidic peat slurry, extrudes pellets, and then bakes the sulfonated peat pellets in an oven at 480-540° C. This baking step drives off the moisture, but it also destroys the carboxylic acid (COOH) groups. His chemical activation of the peat material via the sulfonation step adds sulfonate groups (—SO₃ ⁻) to the resulting peat granules. In use, Clemenson's peat pellets adsorb metals by attaching the metal cations to the sulfonic groups due to their opposite charged states. Clemenson chemically modifies the surface of peat, but failed to preserve carboxylic groups (COOH) that naturally occur in peat. In addition, his invention is lacking of any evidence of improving selectivity to sorb cadmium cations from wastewater in the presence of zinc cations. See also U.S. Pat. No. 6,429,171 issued to Clemenson.

In yet another example, U.S. Pat. No. 5,314,638 issued to Morine discloses a chemically modified peat product that can be used as an ion-exchange material. This peat material is air dried and milled to a size of one mm or less; hydrolyzed in an aqueous hydrochloric acid solution to remove the soluble components (sulfuric acid and nitric acid may also be used); further treated in an extractor with 2-propanol/toluene solvent to remove the solvent-soluble bitumen; dried to remove the residual solvent; and then immersed in a hot concentrated sulfuric acid bath at 100-200° C. for 1-4 hours. This is a chemically-modified peat product. The hot sulfuric acid bath process step comprises chemical modification in which the sulfuric acid reacts with the peat fibers to add sulfonate anions (SO₃ ⁻) to its surface. These anions within the ion-exchange resin attract metals via chemical attachment.

Various efforts have been made within the industry to use granulated and dried peat material as a cation exchange media. More particularly, Soviet Published Patent Application No. 806,615 filed by Peter Illarionovich Belkevich et al. produces a water filter product from pellets comprising a paste made from peat and a precipitate of neutralizing etching solution. This paste and the resulting pellets are produced without any physical activation treatment. Moreover, Belkevich uses his neutralizing etching solution like a glue to hold the peat fibers together in a pellet and therefore obtain the desired granule hardness. Furthermore, Belkevich employs his peat pellets as a filter to remove non-ferrous metals like copper and zinc and petrochemical products from waste water. It is unclear that Belkevich's peat pellets are acting as an ion-exchange material.

Challenges Faced by Peat and Other Natural Organic Materials

But, the large body of available research illustrates the underlying shortcomings for natural peat for use as a sorption medium. In its natural form, peat has low mechanical strength, tends to shrink and swell, and does not allow for hydraulic loading. Moreover, peat and other organic starting materials suffer from a number of other problems that compromise their utility as a sorption medium. For example, prior art activation steps like pyrolysis can cause these materials to lose their ion-exchange capacity. Carbonization may cause considerable shrinkage and weight loss of the materials, as well as loss of natural adsorption properties toward metal ions. Organic sources also generally suffer from non-uniform physical properties. Naturally-occurring organic ion exchange media are unstable outside a moderately neutral pH range. Finally, such natural organic ion exchange media tend to be prone to excessive swelling and peptizing, tend to leach naturally occurring heavy metals into the treated wastewater solution, and do not show evidence of improving selectivity to sorb cadmium cations from wastewaters in the presence of zinc cations, compared with other peat material.

While the processes known in the art for the preparation of sorption material sourced from natural solid organic material like activated carbon have been useful for certain limited adsorption applications, for many other applications it will be necessary to increase the hardness of the ion exchange medium, while minimally sacrificing the media's cation-exchange capacity in the process, minimize leaching of naturally-occurring heavy metals into the treated wastewater solution, and increase the selectivity to sorb cadmium ions in the presence of zinc cations in wastewaters. It is therefore necessary to develop a low-cost process for producing ion-exchange and adsorption media sourced from natural organic starting material exhibiting good natural ion-exchange capacity, increased adsorption capabilities towards heavy metals, minimized leaching of naturally-occurring inorganic and organic compounds, increased selectivity to sorb cadmium ions in the presence of zinc ions, and improved strength so that the medium can be utilized in a wider range of end-use applications, including the removal of heavy metals from industrial wastewaters. It would also be useful to be able to prepare such a sorption media using low processing temperatures without the use of chemical activation with its caustic and corrosive chemicals, and chemical modification with its reliance upon the addition of functional groups to the media to enhance its ion-exchange capacity. Likewise, it would be beneficial to avoid the aggressive chemical modification of the peat or other organic starting material substrate before the chemical activation step.

But, even if a peat or other organic material granule could be produced with appropriate characteristics of hardness and sorption capacity, their use in wastewater cleanup is significantly challenged by the fact that wastewater often includes several different types of metal ions. While a particular granule made from peat or other organic material may efficiently sorb metal ions if they are the only type of metal ions in the wastewater, their performance may markedly deteriorate if two or more types of metal ions are present. Instead of removing a large amount of the toxic first type of metal ion from the wastewater, the active sites on the granules will become filled with metal ions of the second type as well, thereby reducing the capacity of the granules for focusing upon removal of the first type of metal ions. Thus, it would be beneficial to produce a process that can chemically treat the granules after any thermal activation step to enable them to selectively sorb the toxic first type of metal ions over the second type of metal ions that are of less concern for removal. The contribution of selective sorption characteristics to such chemically-modified granules will allow them to target specific metal ion types for removal from the wastewaters on an efficient basis.

SUMMARY OF THE INVENTION

A process for preparation of a granulated or pelletized sorption medium from a partially decomposed organic material like peat, followed by low-temperature thermal activation of the sorption medium to produce a high degree of granule or pellet hardness balanced against an efficacious level of ion-exchange and adsorption capacity, followed by chemical treatment of the sorption material via a preselected solution of soluble salts to increase the availability of naturally-occurring active sites in the granules or pellets to enhance their ion-exchange, complexation, chelation, and adsorption performance to an aqueous solution is provided by this invention (called “APTsorb II*M”). When the granules are used as an ion exchange type medium for treating an aqueous solution like waste waters, the preselected cations from the solution of soluble salts placed on the active sites of the partially decomposed organic material in the sorption medium will alter the coefficient that defines the equilibrium and increase the adsorption capacity more in favor of adsorption of more-toxic metals found in the waste water at the expense of less-toxic metals found in higher concentrations in the waste water. This allows the end user to target the more-toxic metals for adsorption by the sorption medium containing the cations contributed by the preselected solution of soluble salts.

The resulting APTsorb II*M peat granules exhibit a number of beneficial properties when used in a wastewater treatment process where competing toxic metal cations are present in the wastewater. Thus, depending upon the M⁺ cations contributed to the peat granule sorption activity sites by the preselected salt used in the salt solution treatment step, the granules exhibit a selectivity α of a first type of more-toxic metal cations (such as cadmium, lead, copper, or other metals at high concentrations) over a second type of less-toxic metal cations of (such as zinc, aluminum, or iron); greater adsorption activity for the first type of more-toxic metal cations; and greater breakthrough capacity for the first type of more-toxic metal cations. These selectivity, more-toxic metal cations adsorption activity, and more-toxic metal cations breakthrough capacity values will necessarily be dependent upon the competing metal cations that are present in the wastewater to be treated by the APTsorb II*M granule medium. It has been found that the following characteristics should apply to the APTsorb II*M granules:

-   -   Selectivity: 1.62<α≤3.00 when the initial influent concentration         is C_(Cd)=30 ppm and C_(Zn)=30 ppm.     -   Cadmium adsorption activity for the granule: 1.02         ppm<C_(Cd)≤0.209 ppm as measured by the cadmium concentration in         the effluent aqueous solution when the initial influent         concentration is C_(Cd)=30 ppm and C_(Zn)=30 ppm.     -   Zinc adsorption activity for the granule: 1.54 ppm<C_(Zn)≤0.387         ppm as measured by the zinc concentration in the effluent         aqueous solution when the initial influent concentration is         C_(Cd)=30 ppm and C_(Zn)=30 ppm.     -   Breakthrough capacity of 2.99-3.04 mg/g Cd at 50 ppb at 0.1 m/hr         flow velocity and an initial influent concentration of C_(Cd)=5         ppm and C_(Zn)=30 ppm.         It has been found that for a cadmium-only aqueous solution         treated with APTsorb II*Na granules, the breakthrough capacity         of the medium can be as high as 21.32 mg/g Cd at 0.1 m/hr flow         velocity and an initial influent concentration of C_(Cd)=5 ppm         and C_(Zn)=30 ppm. But, if zinc cations are also present in the         aqueous solution to compete with the cadmium cations for the         active sorption sites on the granules, this breakthrough         capacity goes down to 3.00 mg/g Cd at 0.1 m/hr flow velocity and         an initial influent concentration of C_(Cd)=5 ppm and C_(Zn)=30         ppm). However, this diminished breakthrough capacity value is         still six times greater than the 0.47 mg/g Cd value exhibited by         the APTsorb III*Na granules used within the cadmium and zinc         cations competing metals aqueous solution environment.

The sorption medium of this invention can be used in a variety of aqueous solution treatment processes, such as wastewater treatment for removing heavy metal constitutes via ion-exchange and complexation mechanisms, and also reducing the levels of manganese, iron, and other naturally-occurring metals found in the peat substrate from leaching back into the waste water.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 represents a schematic view of the portion of the process for preparing the thermally activated peat granule.

FIG. 2 represents a schematic view of the portion of the process for chemically treating the thermally activated peat granule by means of an acid solution followed by a salt solution to reduce the presence of unwanted minerals within the peat complex, while increasing the sorption capacity and activity of peat granules.

FIG. 3 represents a schematic view of the portion of the process of the present invention for preparing the thermally activated peat granule and chemically treated peat granules that exhibit high selectivity to sorb cadmium cation in the presence of zinc cation (APTsorb II*M).

FIG. 4 represents a graphical depiction of comparative adsorption data for different metal cations contained in aqueous solutions for the non-chemically treated, thermally-activated peat granules (APTsorb II) and its chemically-treated counterpart material (APTsorb III).

FIG. 5 represents a graphical depiction of the cadmium adsorption from an effluent aqueous solution stream containing only cadmium cations using an APTsorb III sorption medium.

FIG. 6 represents a graphical depiction of the cadmium and zinc adsorptions from an effluent aqueous solution stream containing both cadmium and zinc cations using an APTsorb III sorption medium.

FIG. 7 represents a graphical representation of selectivity coefficient to sorb cadmium cations in the presence of zinc cations from aqueous solution containing both cadmium and zinc cations using a different metal-loaded sorption medium. It can be seen that the highest selectivity (2.65) possesses by APTsorb II*Na peat product.

FIG. 8 represents a graphical representation of selectivity coefficient to sorb cadmium cations in the presence of zinc cations from aqueous solution containing both cadmium and zinc cations using a metal-loaded, thermally-activated, and acid treated peat.

FIG. 9 represents a graphical representation of selectivity coefficient to sorb cadmium cations in the presence of zinc cations from aqueous solution containing both cadmium and zinc cations using a metal-loaded, the thermally activated and chemically treated by means of an acid solution followed by a salt solution peat sorption medium (APTsorb III*M). From FIGS. 9-11 it can be seen that the highest selectivity (2.65) possesses by APTsorb II*Na peat product.

FIG. 10 represents a graphical representation of the selectivity of different peat media to adsorb cadmium cations in the presence of zinc cations and activity to adsorb cadmium cation from aqueous solution.

FIG. 11 represents a graphical representation of breakthrough capacity to adsorb cadmium cations in the presence of zinc cations from aqueous solution containing both cadmium (concentration 5 ppm) and zinc (concentration 30 ppm) cations using different media and under 2 different flow velocities.

FIG. 12 represents a graphical depiction of the cadmium adsorption from an aqueous solution stream containing only cadmium and zinc cations at two different flow rates using a sodium-loaded sorption medium of the present invention (APTsorb II*Na).

FIG. 13 represents a schematic depiction of the process for preparing the APTsorb II peat granule media of Example 1.

FIG. 14 represents a schematic depiction of the process for preparing the APTsorb III peat granule media of Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A process for preparation of a granulated or pelletized sorption medium from a partially decomposed organic material like peat, followed by low-temperature thermal activation of the sorption medium to produce a high degree of granule or pellet hardness balanced against an efficacious level of ion-exchange and adsorption capacity, followed by chemical treatment of the sorption material via specially preselected solution of soluble salts to increase its ion-exchange and adsorption performance while minimizing the transfer of natural impurities found in the sorption medium to an aqueous solution, and increase the selectivity to adsorb cadmium cations from wastewaters in the presence of high concentration of zinc cations is provided by this invention. When the granules that contain calcium carbonate in its structure are used as an ion exchange type of medium for treating an aqueous solution like waste waters, the cations placed on the active sites of the partially decomposed organic material in the sorption medium will alter the coefficient that defines the equilibrium and increase the adsorption capacity more in favor of adsorption of major toxic metals found in the waste water at the expense of less toxic metals found in higher concentrations in the waste water. This allows the end user to target the major toxic metals for adsorption by the sorption medium containing the cations contributed by the preselected solution of soluble salts. The sorption medium of this invention can be used in a variety of aqueous solution treatment processes, such as wastewater treatment for removing heavy metal constituents via ion-exchange and complexation mechanisms, and also reducing the levels of manganese, iron, and other naturally-occurring metals found in the peat substrate from leaching back into the waste water.

For purposes of this invention, “partially decomposed organic material” means natural occurring, carbon-based, organic materials that have partially decayed or decomposed over time in the ground, or are plant or animal-based products that are subjected to a bacterial or thermal decomposition process to partially decompose the organic materials therein. Such partially decomposed organic material cover a variety of substances including without limitation compost media (e.g., leaf compost media, peat, plant by-products and combinations thereof), livestock manure, sewage sludge, lignite coal, partially decomposed wood, and combinations thereof. It also includes inorganic substances like apatite (calcium phosphate) and zeolites. Such partially decomposed organic material must also exhibit an ion-exchange capacity between 5-200 mEq per 100 g of organic material, as measured by Barium Acetate Procedure. Compost media is any decayed organic matter. Plant by-products may include partially decomposed plants, leaves, stalks, and silage, for example. Livestock manure is the dung and urine of animals. Sewage sludge is solid, semi-solid, or liquid residue generated by the processes of purification of municipal sewage. Each of the foregoing sources of decomposed or partially decomposed organic matter has innate ion-exchange capacity.

As used in this Application, “aqueous solutions” means any water-based solution containing an environmental impurity as a solute produced by manufacturing, agricultural, or mining industries or population communities. Examples include, without limitation, wastewater discharges; industrial streams; storm water runoffs; mine dewatering streams from mining pits; animal slaughterhouse, cattle-yard, and other agricultural runoffs; spent processing waters emanating from mining, grinding, milling, metallurgical, or extraction process; and hydrofracking.

For purposes of this invention, “impurities,” “contaminants,” or “aqueous contaminants” means any chemical element or compound found in an aqueous solution that poses a health risk to humans or animals, or is otherwise subject to environmental laws or regulations, including without limitation heavy metals like arsenic, lead, mercury, cadmium, manganese, iron, zinc, nickel, copper, molybdenum, cobalt, chromium, palladium, stannum, or aluminum; radioactive materials like cesium or various isotopes of uranium; sulfates, phosphorous, selenium, boron, ammonia, refrigerants, and radon gases.

As used in this Application, “particles” includes any three-dimensionally hardened shaped product formed from the partially decomposed organic material, including, without limitation, granules or pellets.

The term “mEq” means milliequivalents. The equivalent is a common unit of measurement used in chemistry and the biological sciences. It is a measure of a substance's ability to combine with other substances. The equivalent entity corresponding to the transfer of a H⁺ ion in a neutralization reaction, of an electron in a redox reaction, or to a magnitude of charge number equal to 1 in ions. One Eq of a substance is equal to one more divided by the valence of the substance (i.e., the number of electrons that the substance would engage in participating in the reaction). Because, in practice, the equivalent is often very small, it is frequently described in terms of milliequivalents (mEq). A mEq is 1/1000 of an equivalent.

The term “hardness” means a property of the granule medium's ability to resist attrition during handling and operation. The “hardness number” is a measure of this property and is determined by way of the “Ball-Pan Hardness” test. The higher the value, the less the losses in uses. A certain amount of material is put into a pan, together with some steel balls, and shaken for a defined period of time. The material is weighed before and after the shaking to determine the amount of attrition. The percent of original material that remains after shaking is the “hardness number.”

The terms “empty bed contact time” means the time required for a liquid in a carbon adsorption bed to pass through a carbon column, assuming all liquid passes through at the same velocity. It is equal to the volume of the empty bed divided by the flow rate.

The term “sorption” means a variety of chemical mechanisms for removing a chemical element or chemical compound from an aqueous solution, including cation-exchange, complexation, chelation, adsorption, or absorption.

The term “about” means approximately or nearly, and in the context of a numerical value or range set forth herein means±2% of the numerical value or range recited or claimed.

The term “μg” means microgram or one-millionth of a gram or one one-one thousandth of a milligram.

The term “ng” means nanograms or 1×10⁹ grams or 0.000000001 grams.

As used within this Application, “more-toxic metals” means any chemical element or compound found in an aqueous solution that poses a health risk to humans or animals, or is otherwise subject to environmental laws or regulations, including without limitation heavy metals like arsenic, lead, mercury, cadmium, manganese, iron, nickel, copper, molybdenum, cobalt, chromium, palladium, stannum, or aluminum; radioactive materials like cesium or various isotopes of uranium; selenium and boron.

For purposes of this Application, “less-toxic metals” means any chemical element or compound found in an aqueous solution that does not necessarily pose a health risk to humans or animals or is otherwise subject to environmental laws or regulations, including without limitation metals like magnesium, beryllium, strontium, barium, calcium, manganese, copper, zinc, iron, potassium, lithium, as well as ammonium and ammonium groups.

While the sorption medium of the present Application is described using peat as the partially decomposed organic matter starting material, it should be understood that the invention is not limited to peat-based sorption material. Likewise, the end-use applications for the sorption media of the present invention extend well beyond the treatment of heavy metals in wastewater streams described in this Application. They can also serve as solid-phase extraction tools, as well as a chemical useful in the mining industry for concentrating copper.

Production Process for Thermally-Activated Sorption Material

The process for preparing the sorption medium product 10 of the present invention is depicted in FIG. 1 where peat is used as the starting partially decomposed organic material 12. A variety of different types of peat may be used for purposes of this invention, including without limitation, reed sedge, sphagnum peat, high moor peat, transitional moor, and low moor peat. The peat material should be dug from the ground and used in its natural state without any further decomposition process steps. It may, however, be cleaned to remove sticks, stones, and other foreign debris from the fibrous peat material.

Next, finely ground particles of an alkaline earth metal carbonate may be admixed into the peat material 12. Examples include BeCO₃, MgCO₃, CaCO₃, SrCO₃, or BaCO₃, although CaCO₃ (calcium carbonate) is preferred. Such calcium carbonate should preferably have a particle size of about minus 325 mesh. It should be admixed on a weight ratio basis of about 1-5%, preferably 2%, with the peat material 12.

The substantially neutralized peat material 14 is then introduced to a granulating machine 16, such as one sourced from Andritz, Inc. of Bellingham, Wash. The loose, substantially neutralized fibrous peat material 14 will be tossed around inside the drum of the granulator to cause the fibers to adhere to each other, and build up granules of desired size. A binder additive like lignosulfonate may be optionally added to the peat material in the granulator drum to assist this granulation process.

Alternatively, the loose, substantially neutralized peat material 14 may be introduced to an extruder. This extruder will apply pressure to the fibrous material to produce pellets of desired size. Such an extruder may be sourced from J.C. Steele & Sons of Statesville, N.C.

Next, the peat granules or pellets 16 are sent to a dryer 18 such as a belt or rotary dryer sourced from Harris Group of Atlanta, Ga. Using direct heat, the peat granules or pellets will travel through the length of the dryer having an inlet temperature of about 400° C. and an outlet temperature of about 80° C., so that the natural 40% wt moisture level of the peat material contained in the peat granules or pellets will be reduced to about 10-14% wt moisture. Thus, this drying step 18 should be carried out across a temperature range of about 80-400° C. with the preferred temperature of exposure being about 90° C. for about 45 minutes.

The resulting dried peat granules or pellets are then crushed and screened to an appropriate size of about 6 mesh×30 mesh to 30×100 mesh.

The dried peat granules or pellets 18 are then introduced to a thermal activation step 20, also known as “torrefaction.” The peat granule or pellet is put in a jacketed ribbon mixer that has thermal fluid like oil circulating through the jacket. The ribbons are fitted with “lifters,” which pick up the granular peat and drop it through the atmosphere inside the ribbon mixer. This exposure to the hot, inert atmosphere is critical to bringing the granule up to temperature as quickly as possible.

During this heating process, a unique combination of time and temperature are critical for the production of the thermally-activated peat granule (called “APTsorb II” within this Application). Activation (IUPAC Recommendations 1996) can be defined as input of external energy into a chemical system to bring about activation of the system. This activation will initiate or expedite thermochemical reactions. In the instance of this APTsorb II peat granule, heat as a form of energy is first provided by the thermal fluid circulating in the ribbon mixer. This heating process results in the chemical reaction-decomposition of hemicellulose, which occurs naturally in partially decomposed plant matter such as peat. The decomposition of hemicellulose is itself exothermic, as evidenced by a continuing rise in atmospheric temperature even when the heat input of the thermal fluid is stopped. As it decomposes and gives off heat, hemicellulose is converted to highly reactive, cyclic molecules called lactones. Some of these lactones escape the reaction zone along with moisture, but given the correct starting temperature and duration, the bulk of the lactones remain within the reaction zone and undergo a cross-linking polymerization with the natural matrix of the peat. This cross-linking reaction is the result of the exothermic reaction of thermal decomposition of hemicelluloses. It also is the reaction which results in the hardened peat granule called “APTsorb II.”

The term activation itself has several different meanings and nuances. Activation as described by activated carbon, a common filtration media for purification of liquids and gases, is referred to as pyrolysis and carbonization of organic material, which results in the increase of surface area and can be tightly controlled by reagents and temperature to create a material with very specific porosities and physical absorption activity/capacity. It can be achieved by thermal or chemical/thermal reactions.

Thus, the temperature of the thermal fluid is quickly raised to approximately 300-320° C., more preferably 304° C., to thermally activate the peat granules to increase their hardness. The temperature inside the mixer slowly rises as volatiles and contained moisture are driven off. This gasified water and volatile mix constitute the “inert” atmosphere, and work to purge air out of the ribbon mixer.

As the temperature in the atmosphere inside the mixer climbs into the 216° C. range, the rapid breakdown of hemicellulose begins. This is the same reaction as torrefaction of wood. This breakdown of hemicellulose is an exothermic chemical reaction which allows for a rapid rise in the temperature of the atmosphere inside the mixer. The actual temperature of the granule is hard to determine but probably is much lower.

The above reaction is allowed to continue as the temperature is driven into the 271-277° C. temperature range. At this point, the boiler that is used to heat the thermal fluid is turned off. The above reaction releases enough heat to maintain the temperature of the atmosphere in the above range. The process is allowed to continue until approximately 20 minutes have passed where the temperature has been maintained above 271° C.

In the case of the APTsorb II peat granule, the media is described as “partially activated.” This refers to the thermal energy that is delivered to the peat material to initiate the decomposition of hemicellulose in the tightly controlled manner that leads to the increase of structural hardness of the material without losing the natural ability of material to sorb metal ions. If the reaction were allowed to continue past the prescribed time, the resulting material would continue to gain structural hardness but would lose its ability for sorption of metal ions.

This thermal activation process step 20 should preferably be conducted at a temperature inside the activator of about 175-287° C., preferably 200-275° C., more preferably 250° C., and a time period of about 25-90 minutes, preferably 30-60 minutes, for achieving maximum granule hardness. In order to achieve maximum cation exchange capacity in the peat granule, the activation step should be conducted for 25-90 minutes, preferably 25-40 minutes. It has been found that 32 minutes represents an optimal compromise as an activation step time duration for achieving desirable levels of both granule hardness and cation exchange capacity. Note that this activation temperature range is different from the higher 300-320° C. oil temperature used to heat the activator. The thermal heat is applied directly to the dried peat granules 18 without any steam, carbon dioxide, nitrogen, or other inert gas media typically used within the industry in a physical activation process.

In an alternative embodiment, a thermal carrier like steam, carbon dioxide, nitrogen, or other inert gas media can be used in the thermal activation step 20 to deliver the heat as a form of energy to the peat granule. In that case, the gas should preferably be carbon dioxide, and the peat granule should be exposed to it for a time period of about 20-90 minutes, preferably 40-60 minutes. Unlike the physical activation process known in the prior art, this inert gas is not used to oxidize the surface of the peat granule. Instead, it is merely employed as a carrier gas to improve the application of the heat to the peat granule pursuant to the thermal activation step.

Regardless of which method is used to thermally activate the peat granules or pellets, the heating process is stopped at this point, and water is injected in order to rapidly cool the product and stop the reaction. Target moisture for the finished product should be at least 10% so as to prevent the thermally activated peat granules from becoming too hydrophobic. Danger of fire developing within the bagged product is greater if the finished product has less than 5% moisture content.

This thermal activation step results in a hardened media that maintains its structural integrity even when wet, and retains its affinity for metals. The physical appearance of the APTsorb II peat granule is not substantially different from its starting non-thermally-activated material (called “bioAPT”).

The degree of granule hardness for the resulting thermally-activated peat granule 22 of the present invention should have a Ball-Pan Hardness number of about 75-100%. More preferably, this Ball-Pan Hardness number should be about 80-98%. Depending upon the specific end-use application for the peat granule 22, a person skilled in the art will be able to determine the necessary hardness value falling within this range.

The peat granules thermally activated in the manner described in this Application will exhibit a copper cation-exchange capacity (“Copper CEC”) of about 120 mEq/100 g of Cu²⁺ at a thermal activation temperature of about 232° C., while a 287° C. temperature condition produces a partially activated peat granule with a cation-exchange capacity of about 92 mEq/100 g of Cu²⁺. Untreated peat has a natural copper cation-exchange capacity of about 120 mEq/100 g of Cu²⁺. Thus, cation-exchange capacity suffers at relatively higher thermal activation temperatures within the 232-287° C. range, and granule hardness is improved at activation times up to 60 minutes, while degrading after 90 minutes and at temperatures above 287° C. Thus, this invention provides a tradeoff between granule hardness and cation-exchange capacity.

There is significant shrinkage in the actual size of the individual thermally-activated peat granules, so they are screened again across a 30 mesh screen. Losses due to shrinkage under the process of the present invention are typically 15%.

Without wanting to be bound to any particular chemical theory, it is believed that this thermal activation step comprises torrefaction of the peat granule, which necessarily requires lower temperatures like the preferred 200-275° C. range identified above. According to a glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996), activation can be defined as the input of external energy into a chemical system to bring about activation of the system. As commonly understood within the industry, “torrefaction” is a medium-temperature, thermochemical process, commonly carried out around 250-300° C., which significantly improves the grindability of wood and straw. Peat naturally has carbohydrates in it, which undergo a thermochemical decomposition to produce lactones, which are then broken down into hydroxy acids that react with natural polymers found within the peat material to cross-link, and as a result to harden the peat granule. At the same time, this relatively low-temperature range for the thermal activation step will preserve enough of the natural ion exchange capacity of the peat material to preserve the efficacy of the resulting ion exchange medium. This combination of increased peat granule hardness and preserved ion exchange capacity renders the peat product of the present invention an ideal, natural ion exchange medium for removing heavy metal cations from waste water. Thermal activation is normally applied in the industry to activated carbon material to increase its surface area.

Note that this 200-275° C. thermal activation temperature range of the present invention is considerably lower than the temperatures normally associated with conventional physical activation and chemical activation. In the case of physical activation, the starting material for, e.g., activated carbon, will first be carbonized by pyrolyzing it at a high temperature generally within the range of 600-900° C. in an inert, oxygen-depleted atmosphere using gases like argon or nitrogen, followed by an activation step in which the carbonized material is exposed to an oxidizing atmosphere provided by, e.g., carbon dioxide, oxygen, or steam at a high temperature usually within the range of 600-1200° C. This carbonization step produces a large number of micropores within the surface of the carbonaceous starting material. The physical activation step is used to drive off chemical compounds which might clog these pores. Thus, the very high temperatures of physical activation are used to increase the hydrophobic adsorption capacity of the starting material. But these high temperatures will also tend to soften the carbonized and activated carbon particles, and destroy the cation-exchange properties.

As for the conventional case of chemical activation, when some of the energy required for a reaction is provided by a preceding exothermic chemical reaction, there is said to be “chemical activation.” For chemical activation, pyrolysis char, carbonized product, or carbonaceous material would be impregnated with some chemical reagents, such as phosphoric acid, zinc chloride, alkaline hydroxides, and ferric chloride. Under conventional chemical activation, the material can be then carbonized at a lower temperature (e.g., 450-900° C.), which is still significantly high compared against the 200-275° C. partial activation temperature range of this invention. This heat treatment will destroy the cation-exchange sites of the material.

As for the conventional case of chemical modification, the carbonaceous material will be treated with, e.g., sulfuric acid to increase its cation-exchange sites by adding SO₃ ⁻ groups to the surface structure to improve the cation-exchange capacity. But once again this chemical modification process would be employed to increase the cation-exchange capacity while decreasing the hardness of the carbonaceous material without preserving the natural cation-exchange properties of the peat material. By materially softening the peat granules or pellets, it therefore would become necessary to reform the granules or pellets with the assistance of a binder additive after the activation step.

Indeed, the process of the present invention does not employ chemical activation, nor chemical modification. Instead, the process of the present invention seeks to partially activate the peat granules to an incomplete degree using relatively low temperatures for a relatively limited time period, without addition of chemical groups via chemical modification in order to increase granule hardness while maintaining or at least minimizing the decrease in cation-exchange capacity of the heat-activated peat material.

By itself, the APTsorb II thermally-activated peat granule 22 provides in combination a desired degree of granule hardness that prevents the medium from becoming damaged during a wastewater treatment process, along the a sorption activity level that is sufficient to remove a good portion of the toxic metal ions from the wastewater. This relatively low-cost peat granule medium is the subject of U.S. Pat. Nos. 8,232,225 and 8,685,884, both granted to American Peat Technology, LLC.

Chemical Treatment Process for the APTsorb III Sorption Medium

A challenge faced by the wastewater treatment industry is the fact that some toxic metals like cadmium often are present in wastewaters at relatively lower concentrations on the order of 10 ppb. But due to their serious toxicity level, government regulatory standards require even lower concentrations of cadmium which creates the need for a peat granule product exhibiting an even greater sorption activity for cadmium and other seriously toxic metals, while minimizing leaching of other metals from the parent material.

A chemically-treated, thermally-activated sorption medium called “APTsorb III” previously developed by the same co-inventors of this Application and the subject of separate patent application U.S. Ser. No. 13/841,526 filed on Mar. 15, 2013 fills this need. This chemical treatment process 30 occurs after the thermal activation step 20, as shown in FIG. 2. First, the peat granules are immersed in an acid solution like a 1 molar (lesser or greater) solution of hydrochloric acid, formic acid, acetic acid, sulfuric acid, nitric acid, or phosphoric acid. The resulting chemical reactions for this acid solution treatment step 32 can be carried out at room temperature, but proceed much faster (and more cost effectively) at elevated temperatures. Favorable results are obtained at temperatures as high as 100° C. (210° F.). At the upper end of this temperature range, reaction time can be shortened from 24 hours to 10 minutes. The acid solution will dissolve the mineral forms of calcium, manganese, iron, and possibly other metals.

This acid solution treatment step seeks to remediate one of the intrinsic flaws of natural peat. Peat material has been formed by nature in a metal-enhanced environment. The ground and surface waters that feed wetland systems are generally rich in minerals and metals. In particular, the waters of northern Minnesota, because of the geology of the region, have raised concentrations of manganese. Manganese is a benign metal abundant in the glacial till that was uniformly deposited across the upper Midwest during the last glacial events. Manganese has a complicated chemistry and readily morphs between dissolved and mineral forms depending on the chemical matrix of the water.

As peat forms, manganese is accumulated in two ways. First, the dissolved form of the metal is adsorbed onto the active sites of the organic surface and held there by chemical bonds. Second, dissolved manganese precipitates inside the peat matrix and results in the accretion of interstitial minerals. Both types of accumulation result in increased manganese concentrations of the natural peat.

Following the acid solution reaction step 32, the acid-treated peat granules are rinsed with water in either a batch process or continuous process to remove metal ions from pore spaces and surfaces of the peat granule until the test for the presence of calcium ions is negative. This rinse step 34 can be conducted at room temperature, but is more cost-effectively done at temperatures as high as 93° C. (200° F.). The manganese, calcium, and other cations, as well as residual acid are removed from the peat granule surface. This rinsing step is repeated one more time, preferably six more times, or until the test for presence of calcium and/or chloride ion is negative.

Following this rinse step 34, metal ions (comprising mostly calcium, manganese and iron ions) need to be removed from the complexation and ion exchange sites (where they are weakly held) on the internal and external surfaces of the peat granule. This is accomplished by immersing the peat granule in a 1 molar (lesser or greater) solution of sodium chloride or other salt solution of Na⁺, Li⁺, K⁺, or Cs⁺. Again, these chemical reactions for this salt solution treatment step 36 can be carried out at room temperature, but proceed much faster (and more cost-effectively) at temperatures as high as 100° C. (210° F.). At the upper end of this temperature range, reaction time can be shortened from 24 hours to 90 minutes. The salt solution will displace the metal ions from the complexation and ion exchange sites in much the same way as sodium or magnesium ions are used to displace metal ions in the regeneration of standard ion exchange resins.

Following this salt solution treatment step 36, the peat granules are rinsed in water to remove the residual salt solution and any remaining metal ions from the internal and external surfaces of the peat granule. This rinse step 38 should be continued until the concentration of chloride ions is down to an acceptable level. Again, this can be done at room temperature, but proceeds at a much faster rate at a temperature of about 100° C. (210° F.).

The finished peat granule APTsorb III sorbent medium 40 following the chemical treatment process 30 will exhibit approximately the same granule hardness as for the thermally-activated granule produced by process 20. Thus, this chemical treatment process does not diminish the important peat granule harness properties achieved through thermal activation.

The final thermally-activated, chemically-treated peat APTsorb III product will typically have a granular size distribution as shown below in Table 1 with about 95% of the granules falling within the 16-50 mesh size range.

TABLE 1 Stays on: APTsorb III batch # 05.12.11 10 mesh   0% 16 mesh 21.0% 20 mesh 34.0% 30 mesh 24.7% 50 mesh 14.8% Bottom pan  5.0%

The Ball-Pan Hardness value for the thermally-activated, chemically-treated APTsorb III peat granules will be about 75-90%, preferably 80-90%. Such granules will exhibit stability without losing their ability to adsorb metals in an aqueous environment at pH=1-8.

Sorption activity is measured in different ways for the thermally-activated, chemically-treated APTsorb III peat granule product. Unlike the copper CEC method used for the thermally-activated, non-chemically-treated APTsorb II product 22, the capacity and activity for the finished thermally-activated, chemically-treated APTsorb III product 40 is measured through a 24-hour equilibrium with a 30,000 ppb cadmium solution in a 1:100 (w/v) ratio. Following the equilibrium and filtering, the peat granule filtrate is analyzed for cadmium concentration, as a measure of adsorption activity generally, using cadmium as a proxy. A higher concentration result translates into a granule with less CEC and activity. Granules chemically treated in the manner described for the APTsorb III product under this invention will typically have equilibrium filtrates between 50 and 200 ppb cadmium, while increasing the active sites on the peat granule surface and capacity of those granules for heavy metal cation affinity, while also minimizing the biological oxygen demand in the treated waste water. These last three characteristics are produced by the acid solution reaction step 32 and salt solution reaction step 36. The acid solution treatment step 32 and salt solution treatment step 36 displace Ca⁺² and Mn⁺² ions that are occupying complexation and ion exchange sites on the internal and external surfaces of the peat granules. This results in a net increase in CEC, increased in-site activity, and reduced leaching of organic molecules, as well as heavy metal contaminants, such as manganese, iron, etc. Thus, the removal of the Ca⁺² and Mn⁺² ions from the peat media by means of the acid solution treatment step and consequent freeing up of active sorption sites on the peat media surface directly contribute to the increased sorption activity for toxic metals like cadmium that is a critical feature of the APTsorb III product.

Cadmium adsorption capacity represents another methodology for measuring sorption activity of the thermally-activated, chemically-treated peat granules. If the granules are placed in an aqueous water solution having a 50 ppb cadmium concentration, over time an equilibrium between cadmium ions moving between the granules and aqueous solution will be reached. There will be about 10-20 mEq Cd/100 g peat material at this 50 ppb Cd concentration in the aqueous solution, preferably 15-18 mEq Cd/100 g peat material. This measures the ability of the peat granules to adsorb cadmium at low equilibrium concentration in the solution.

Just as importantly, by reducing the presence of manganese cations naturally found in the peat granules, less manganese can leach into the waste water stream during treatment with the thermally-activated, chemically-treated peat granules 40 of the present invention. APTsorb III granules prepared as described herein will leach less than 5 ppb manganese, preferably less than 1 ppb manganese, into water when acting as an ion-exchange medium in a column contactor. Manganese is a contaminant whose presence should be controlled in potable water. Still another characteristic of the thermally-activated, chemically-treated APTsorb III peat granule product is its maximum measured loading capacity for cadmium ions. This value is 35-50 mEq/100 g at almost unlimited Cd⁺² concentration dosing, preferably 40-45 mEq/100 g. Hence, the APTsorb III sorbent medium 40 retains much of its inherent cation-exchange capacity, obtains an increased capacity for metals in solution, and has increased strength and durability when exposed to water, and less leaching of organic molecules. These characteristics make the media well-suited for waste water remediation, and other treatments of aqueous and non-aqueous solutions to remove contaminants and impurities present in wastewaters at lower concentration levels.

Chemical Treatment Process for the APTsorb II*M Sorption Medium

Yet another challenge provided within the wastewater treatment industry is the fact that the wastewaters rarely contain a single type of metal. Two or more types of metal cations may be present. Because all of these metal cations compete for the same active sorption sites on the surface of the peat granule, neither the APTsorb II thermally-activated granules, nor the APTsorb III thermally-activated, chemically-treated granules may succeed in adsorbing a sufficient portion of each type of metal cations within the wastewater to bring them below the imposed regulatory limits. In mining wastewater applications where higher concentrations of zinc are present in combination with lower concentrations of cadmium, the more serious need is to target the more-toxic cadmium cations over the zinc cations by the wastewater treatment process. For example, it has been discovered that the APTsorb III*M granules produced a breakthrough capacity of 16.49 mg/g Cd when used to treat a cadmium cations-only aqueous solution (Example 5). But this breakthrough capacity value plummeted to 0.47 mg/g Cd when the APTsorb III*M granules were used to treat a cadmium and zinc cations competing metals aqueous solution environment (Example 6).

Thus, the present invention of this Application produces a thermally-activated, chemically-treated metal form of the APTsorb II peat granules (“APTsorb II*M”) that provides a beneficial combination of granule hardness, selectivity for a first type of metal cations (e.g., cadmium) over a second type of metal cations (e.g., zinc), a high activity for adsorption of the first type of metal cations, and a high level of breakthrough capacity for loading the first type of metal cations onto the active surface sites of the peat granule. The achievement of the high sorption activity and breakthrough capacity characteristics of this APTsorb II*M sorption medium is all the more surprising in light of an omission of the acid solution treatment step employed in the APTsorb III product process 30 that was used to remove calcium and manganese from the peat medium to free up active sites on the peat medium to enhance adsorption activity and breakthrough capacity.

In aqueous solutions containing high concentrations of cadmium, the thermally-activated and chemically-treated sorption medium discussed above will treat the aqueous solution in accordance with Reaction I shown below:

The metal cations M⁺ located on the peat granule active sites, which are described above as being Na⁺ resulting from the sodium chloride salt solution used to chemically treat the sorption medium, will be displaced by the cadmium (Cd²⁺) cations found in the aqueous solution during the ion exchange treatment process with the result that the cadmium cations are absorbed by the peat granules with the benign Na⁺ cations dispersed in the treated aqueous solution.

The presence of these M⁺ cations on the active sites of the peat granules will alter the coefficient that defines the equilibrium and influences the adsorption capacity more in favor of Cd²⁺ adsorption by the sorption medium at the expense of Zn²⁺ adsorption. In addition, the presence of CaCO₃ or other alkaline earth metal carbonate (e.g., BeCO₃, MgCO₃, CaCO₃, SrCO₃, or BaCO₃) in the peat media is believed to interact synergistically with the M⁺ cations and peat material to further increase the selectivity, activity, and adsorption capacity characteristics of the APTsorb II*M granules in favor of Cd²⁺ cations. This will allow the end user to target Cd²⁺ adsorption to leave more of the Zn²⁺ cations in the aqueous solution during the treatment process by means of selecting a sorption medium for which a special preselected solution of soluble salts was used that favors Reaction I over Reaction II.

The process for producing the APTsorb II*M sorption medium is shown in FIG. 3. The thermally-activated peat granules 22 having a desired degree of hardness and cation exchange capacity characteristics are treated to a chemical treatment process 50 after the thermal activation step. First the peat granules are immersed in a sodium chloride or other salt solution of a metal cation Me. These chemical reactions for this salt solution treatment step 52 can be carried out at room temperature, but it will proceed much faster (and more cost effectively) at temperatures as high as 100° C. (210° F.). At the upper end of this temperature range, reaction times can be shortened from 24 hours to 90 minutes. The salt solution will displace metal ions comprising mostly calcium, manganese, and iron from the complexation and ion exchange sites on the peat granules in much the same way as sodium or magnesium ions are used to displace metal ions in the regeneration of standard ion exchange resins.

Following this salt solution treatment step 52, the peat granules are rinsed in water to remove the residual salt solution and remaining metal ions from the internal and external surfaces of the peat granule. This rinse step 54 should be continued until the concentration of the anion constituent of the salt is down to an acceptable level. Again, this can be done at room temperature, but it proceeds at a much faster rate at a temperature of 100° C. (210° F.).

Finally, the rinsed peat granules bearing the M⁺ cations contributed by the salt solution are dried for about 24 hours. This drying step 56 is carried out at a temperature around 105° C.

The finished APTsorb II*M peat granules 58 following the chemical treatment process 50 will exhibit approximately the same granule hardness as for the thermally-activated APTsorb II granules 20. Thus, this chemical treatment process does not diminish the important peat granule hardness properties achieved through thermal activation. But at the same time, the resulting APTsorb II*M peat granules 58 exhibit a number of other beneficial properties for use of the APTsorb II*M peat granules in a wastewater treatment process where competing toxic metal cations are present in the wastewater. Thus, depending upon the M⁺ cations contributed to the peat granule sorption activity sites by the preselected salt used in the salt solution treatment step 52, the granules exhibit a selectivity α of a first type of more-toxic metal cations (such as cadmium, lead, copper, or other metals at high concentrations) over a second type of less-toxic metal cations of (such as zinc, aluminum, or iron); greater adsorption activity for the first type of more-toxic metal cations; and greater breakthrough capacity for the first type of more-toxic metal cations. These selectivity, more-toxic metal cations adsorption activity, and more-toxic metal cations breakthrough capacity values will necessarily be dependent upon the competing metal cations that are present in the wastewater to be treated by the APTsorb II*M granule medium. According to Examples 7 and 8 of this Application, for wastewater containing cadmium cations and zinc cations, it has been found that the following characteristics should apply to the APTsorb II*M granules:

-   -   Selectivity: 1.62<α≤3.00 when the initial influent concentration         is C_(Cd)=30 ppm and C_(Zn)=30 ppm.     -   Cadmium adsorption activity for the granule: 1.02         ppm<C_(Cd)≤0.209 ppm as measured by the cadmium concentration in         the effluent aqueous solution when the initial influent         concentration is C_(Cd)=30 ppm and C_(Zn)=30 ppm.     -   Zinc adsorption activity for the granule: 1.54 ppm<C_(Zn)≤0.387         ppm as measured by the zinc concentration in the effluent         aqueous solution when the initial influent concentration is         C_(Cd)=30 ppm and C_(Zn)=30 ppm.     -   Breakthrough capacity of 2.99-3.04 mg/g Cd at 50 ppb at 0.1 m/hr         flow velocity and an initial influent concentration of C_(Cd)=5         ppm and C_(Zn)=30 ppm.         It has been found that for a cadmium-only aqueous solution         treated with APTsorb II*Na granules, the breakthrough capacity         of the medium can be as high as 21.32 mg/g Cd at 0.1 m/hr flow         velocity and an initial influent concentration of C_(Cd)=5 ppm         and C_(Zn)=30 ppm. But, if zinc cations are also present in the         aqueous solution to compete with the cadmium cations for the         active sorption sites on the granules, this breakthrough         capacity goes down to 3.00 mg/g Cd at 0.1 m/hr flow velocity and         an initial influent concentration of C_(Cd)=5 ppm and C_(Zn)=30         ppm (Example 8). However, this diminished breakthrough capacity         value is still six times greater than the 0.47 mg/g Cd value         exhibited by the APTsorb III*Na granules used within the cadmium         and zinc cations competing metals aqueous solution environment         (Example 6).

For purposes of these calculations, the distribution coefficient of Zn²⁺ cation is calculated using the following formula:

C_(Zn solid)—concentration of Zn²⁺ ions, which was sorbed on the peat granules, mmol/g. C_(Zn solution)—concentration of Zn²⁺ ions in a solution after equilibrium, mmol/L. Similarly, the distribution coefficient of Cd²⁺ cation is calculated using the following formula:

$\lambda_{Cd} = \frac{C_{{Cd}\mspace{20mu}{solid}}}{C_{{Cd}\mspace{14mu}{solution}}}$ C_(Cd solid)—concentration of Cd²⁺ ions, which was sorbed on the peat granules, mmol/g. C_(Cd solution)—concentration of Cd²⁺ ions in a solution after equilibrium, mmol/L. Next, the selectivity values for Cd²⁺ ions over Zn²⁺ ions for the various samples are calculated as follows:

λ_(Cd)—distribution coefficient of Cd²⁺ cation. λ_(Zn)—distribution coefficient of Zn²⁺ cation.

For purposes of this invention, this special preselected solution of soluble salts used in step 52 comprises any compound having a cation constituent and an anion constituent where:

-   -   the cation constituent is selected from the group consisting of         any 1⁺ or 2⁺ cation of, e.g., ammonium (NH₄ ⁺), ammonium groups         (NR₄ ⁺), sodium, potassium, lithium, cesium, beryllium,         magnesium, calcium, barium, manganese, copper, zinc, strontium,         or iron; and     -   the anion constituent is selected from the group consisting of         SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, NO₃ ⁻, NO₂−, PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻,         Cl⁻, I⁻, Br⁻, F⁻, HCOO⁻, CH₃COO⁻, C₂H₅COO⁻, C₃H₇COO⁻, C₄H₉COO⁻,         ClO₄ ⁻, HCO₃ ⁻, or CO₃ ²⁻.         Sodium represents the preferred cation constituent form for the         preselected soluble salt solution with chloride (NaCl) being         used.

Because these particular cations represent less toxic metals, their placement on the active sites of the sorption medium via the salt solution treatment step 52 to enable the sorption medium to adsorb a major toxic metal like cadmium, while leaving most of the less toxic metals in the aqueous solution during the treatment process will produce a much greater adsorption capacity of the sorption medium for the major toxic metal, as measured by the breakthrough capacity. This modified salt solution treatment step for the sorption medium using the preselected solution of soluble salts should result in an improved breakthrough capacity for cadmium in a single metal aqueous solution according to a performed experiment of up to 21.32 mg/g at 50 ppb of the major toxic metal based upon a 0.1 m/hr flow velocity and an initial influent concentration C_(Cd)=6 ppm.

While the calcium carbonate or other alkaline earth metal carbonate compound described above represents a preferred embodiment of this invention, because of the belief that it synergistically interacts with the M⁺ cations and peat material in the APTsorb II*M granules to increase the selectivity, sorption activity, and breakthrough capacity characteristics for the more-toxic metal cations contained in the wastewaters treated with the APTsorb II*M product, other compounds may be used in lieu of the calcium carbonate or other alkaline earth metal carbonates to achieve these objectives. For example, limestone or Ca(OH)₂ may be added to the peat during production of the APTsorb II granules used to produce the APTsorb II*M product. Alternatively, a non-water soluble salt of polyprotic acids (preferentially weak polyprotic acids) might work. Such a non-water soluble salt should be made out anions of polyprotic acids such as PO₄ ³⁻, HPO₄ ²⁻, H₂PO4⁻, SO₄ ²⁻, HSO₄ ⁻, C₂O₄ ²⁻ (oxalic acid), HC₂O₄ ⁻, C₆H₈O₄ ²⁻ (adipic acid), C₆H₉O₄ ⁻ (adipic acid), C₆H₄(COO)₂ ²⁻ (phthalic acid), or C₆H₄C₂O₄H⁻; and cations of an alkaline earth metal cations such as Ca²⁺, Mg²⁺, Be²⁺, Ba²⁺, or Sr²⁺. All of these different compounds are referred to for purposes of this Application as “synergistic interactive agents.”

The following examples illustrate the process of the present invention for producing the APTsorb III sorbent medium 40 from partially decomposed organic matter using low-temperature thermal activation and the acid solution and salt solution chemical treatment steps. Other examples illustrate the process of the present invention for producing the APTsorb II*M sorbent medium 58 from the partially decomposed organic matter using low-temperature thermal activation and the salt solution chemical treatment steps, and its beneficial selectivity, adsorption activity and breakthrough capacity characteristics.

Example 1—Process for Producing Thermally-Activated “APTsorb II” Peat Granules

As depicted in Fig. 13, the APTsorb II peat granule media was prepared using peat of a reed-sedge type commercially available from American Peat Technology, LLC of Aitkin, Minn. The raw peat material was first dried to a moisture content of about 40% wt. Calcium carbonate (2% by weight) was added to raw peat and the mixture was extruded into pellets, dried again to reduce the moisture content to about 12% wt, and finally crumbled and sieved. This process resulted in a multifunctional granular media called “bioAPT.”

The finished bioAPT peat granule with a size range of 10×30 mesh was then thermally activated to produce the APTsorb II media. The bioAPT granules were introduced into a jacketed ribbon mixer. The mixer had thermal fluid circulating through the jacket at a temperature of about 300° C., thereby effectively heating the atmosphere inside the mixer. Additionally, the mixer ribbons were fitted with “lifters” that picked up the media and dropped it through the heated atmosphere. Also, the design of the mixer and the resulting chemical reactions resulted in an oxygen-free atmosphere inside the mixer. The bioAPT material was heated and mixed within this oxygen-free atmosphere for approximately 32 minutes, at which point the chemical reactions necessary for thermal activation were complete, and the granular media was converted into the APTsorb II media. This media was then quickly cooled, using a water spray, and the moisture content was adjusted to about 10% wt moisture level.

Four production trials of the APTsorb II peat granules were recorded and tested for quality control purposes. Observations with respect to activation temperatures, product yield, copper cation exchange capacity, and ball-pan hardness were made as shown in Table 2.

TABLE 2 Copper Cation- Activation Activation Outlet Product Exchange Ball-Pan Temp Time Temp Yield Capacity Hardness Sample (° C.) (min) (° C.) (wt. %) (mEq/100 g) (%) Reed-Sedge 132 5 Peat BioAPT 148 85.7 APTsorb II 302 32 200 83 134 96 Run 1 APTsorb II 315 32 204 85 135 97 Run 2 APTsorb II 304 34 203 83 140 95 Run 3 APTsorb II 302 40 201 81 125 97 Run 4]

A modified ASTM D3802-10 standard test method was used for purposes of measuring Ball-Pan Hardness of the thermally-activated APTsorb II peat granules. The moisture content of the media was measured using a Mettler Toledo MJ33 moisture meter. Water was then added to 200 g media in order to bring the moisture content to 35% wt. The media was mixed thoroughly and kept for 15 min at room temperature. At the end of the equilibrium period, the media was free-flowing and not sticky, indicating that the correct moisture content had been reached. One hundred thirty grams of the moistened media was screened on a 50 mesh sieve shaker for 3 minutes. A 100 g sub-sample (A in the formula) of media after screening (usual particle size is 10-50 mesh) was placed in the sieve catch pan, and 36 steel balls (15.9 mm diameter, 16.3 g each) were added. The catch pan was covered, and the sub-sample was shaken for 6 minutes to approximate abrasion and attrition. Following this abrasion step, the steel balls were removed, and the media was screened again on a 50 mesh sieve for 5 minutes. The amount of media retained on the 50 mesh screen was recorded in grams (B in the formula).

The Ball-Pan Hardness number was calculated using the following equation: H=B/A×100 where:

-   -   H=Ball-Pan Hardness number     -   B=weight of sample retained on hardness test sieve after the         abrasion step (g)     -   A=weight of sample loaded onto hardness pan prior to the         abrasion step (g).         Generally, a higher Ball-Pan Hardness number indicates a harder         granule that is more resistant to abrasion. A lower Ball-Pan         Hardness number generally indicates that more media is abraded         by the steel balls and is less durable.

The method used to measure the cation-exchange capacity (“CEC”) of the thermally-activated APTsorb II peat granules was a modification of the usual CEC methodology, and represents a concession to the need for speed in the industrial research lab. The exchange of cations on the surface of the media is measured using the media as produced, without first converting the surface to an H⁺ form, and the indication of exchange is measured by the concentration of the exchanging ion before and after contact with the media. The exchanging ion in this case is copper, prepared as a 1000 ppm solution of copper using copper chloride, buffered to a pH of about 4.8. The buffer solution was prepared by adding 1.68 ml of glacial acetic acid and 9.51 g of sodium acetate trihydrate to Type I deionized water and diluting to 1 L. The buffer solution was then used to make the 1000 ppm copper solution by dissolving 2.683 g of CuCl₂*2H₂O in the 1 L of buffer solution.

The media was dried on a Mettler Toledo MJ33 moisture meter at 160 degrees ° C. until its weight was stable for 30 seconds. One gram of the dried media was then added to 100 ml of the 1000 ppm copper solution, and the mixture was stirred at around 300 RPM for 3 hrs at room temperature. The flask and stirring rod were positioned so that the rod made contact against the wall of the flask, thereby effectively pulverizing the media over the course of the stirring period. The mixture was filtered and the concentration of Cu²⁺ was measured by colorimetry or by graphite furnace atomic absorption spectroscopy. The cation exchange capacity of the media was calculated using the following formula: CEC,mEq/100 g=(I−F)*20/63.5 where:

-   -   I=initial concentration of copper in the solution (ppm).     -   F=final concentration of copper in the solution (ppm).

The results shown in Table 2 demonstrate the repeatability and consistency of the thermal activation method for producing the APTsorb II granule under this invention.

Example 2—Chemical Treatments of the Thermally-Activated APTsorb II Peat Granules to Produce the APTsorb III Peat Granule

The process used to produce the chemically-treated, thermally-activated sorption medium called “APTsorb III” is illustrated in the schematic drawing shown in Fig. 14. A 2 L volume of a 1N solution of HCl was added to 1 kg of the APTsorb II media at room temperature. The mixture was kept at room temperature for 24 hrs with periodic shaking in such a fashion so as not to destroy the granules. The pH was maintained at a value of 2 or lower. This acid treatment was completed when the concentration of calcium, manganese and other bivalent ions reached maximum concentrations in the solution as determined by the titration procedure described below. The mixture was filtered and washed six times with water or until the test for the presence of chloride ions in the filtrate, as described below, was negative. The volume of combined acid and rinsing solutions was 11 L.

Following the acid treatment, 5 L of 1M solution of NaCl was added to the media, and the mixture was refluxed for 90 minutes. Following the reflux period, the mixture was filtered while it was still hot and washed with water until the test for the presence of chloride ions in the filtrate was negative. The volume of combined salt and rinsing solutions was 8 L.

The solid part was dried at 105° C. for 24 hrs to yield 760 g of thermally-activated and chemically-treated granular peat media called APTsorb III. Samples of the APTsorb III material were subjected to the quality control (QC) test as described below. The material balance for the chemical treatment steps is shown in Table 3.

TABLE 3 Example of material balance for APTsorb III production. Reagents Amount APTsorb II (11.2% H₂O) 1000 g 1N HCl 2 L Rinsing with H₂O 11 L 1M NaCl 5 L Rinsing with H₂O 8 L APTsorb III (QC = 160 ppb) product 760 g The removal of the organics and chloride ions by the aqueous solution at 180° C. accounts for the reduction of mass for the APTsorb III peat granules.

The tests referred to above are critical for the production of the APTsorb III peat granules. If the bivalent ion concentration in the acid solution does not reach maximum while the solution pH remains below 2, it indicates that the mineral fraction that naturally occurs in the parent peat material is incompletely removed. The incomplete removal of this mineral fraction results in the leaching of manganese and calcium later when the product is utilized as a filtration media. Also, the acid treatment results in the exchange of metals for hydrogen ions on the active surfaces of the peat material, thereby “cleaning” the impurities inherent in the parent peat material.

The following titration procedure was used to measure the concentration of calcium, manganese, and other bivalent ions contained in the HCl solution that were removed from the APTsorb II material: An ammonium buffer was prepared by adding 20 g of ammonium chloride and 74 ml of ammonium hydroxide (28-30% NH₃) to a flask and diluting it to 1 liter with Type 1 deionized water. The pH of the buffer was 10.02. Ten milliliters of the HCl acid treatment filtrate was added to an Erlenmeyer flask and diluted with 50 ml of Type I deionized water. The pH was adjusted to slightly acidic (pH=4-6) if necessary by the addition of a 5% solution of NH₄OH in deionized water or 1N HCl. An excess of 0.1N solution of EDTA in water was added, swirled, and kept at room temperature for 20 minutes to allow for complete complexation between the EDTA and bivalent ions present in the acid treatment filtrate. Three milliliters of a 4% solution of triethanolamine in type I deionized water was added and swirled. Ten milliliters of the ammonium buffer solution was added so that the pH of the solution was 10.

Immediately, 5-10 drops of an indicator solution of eriochrome black T was added, and the mixture was titrated with a 0.1N solution of MgCl₂ in deionized water until the color changed from blue to pink/red.

The concentration of bivalent ions in the sample was calculated as follows:

$C_{Sample} = \frac{\left( {C_{EDTA} \times V_{EDTA}} \right) - \left( {C_{{MgC}\; 12} \times V_{{MgC}\; 12}} \right)}{V_{Sample}}$

The following test was used to detect the presence of chloride ions in the rinsing water: Five tenths milliliter of a 1% solution of silver nitrate was added to a 20 ml sample of rinsing water. If chlorides were present, a white precipitate in the form of silver chloride formed immediately, which evidenced the need for additional rinsing.

The following cadmium equilibrium quality control test (“QC test”) method was used to measure the adsorption activity of peat granules. One gram of dried media was added to 100 ml of a 30 ppm solution of Cd²⁺ in Type I deionized water. The equilibrium was rolled at 8 rpm at room temperature (20±2° C.) in a leak-proof vessel for 24 h. The mixture was filtered using 0.45 μm polypropylene syringe filter membrane. The liquid fraction was preserved by adding concentrated HNO₃ and analyzed by GFAA spectroscopy for the concentration of Cd²⁺ and Mn²⁺ ions. This procedure measures the activity of the media: a lower concentration of Cd²⁺ in the solution translates into more of the cadmium being adsorbed onto the media and thereby indicates greater sorption activity.

Example 3—Adsorption Characteristics of APTsorb III Peat Granules

The APTsorb III peat granules for this experiment were produced by mixing 500 g of APTsorb II material and 1 L of 1 N HCl. The mixture was kept at room temperature for 24 h with periodic shaking, so as to not destroy the granules. After the acid treatment, the media was rinsed with deionized water until the filtrate was free of chlorides as described in the test above. The media was then mixed with 5 L of 1 M NaCl solution and heated. The mixture was held at 90-100° C. for 90 minutes, filtered while still hot, and rinsed until free of chlorides as described above. The treated media was then dried for 24 h at 105° C.

The adsorption activity of the APTsorb III material was measured by the cadmium equilibrium QC test. Filtrates were preserved and analyzed for manganese and cadmium, using graphite furnace atomic absorption spectrometry. The results are shown in Table 4 below.

TABLE 4 Concentration of Mn and Cd after QC test with initial concentration of Cd equal 30,000 ppb. Raw reed- APTsorb III APTsorb III sedge peat APTsorb II 1 kg scale 500 lb scale C_(Cd), ppb 1200 1400 160 50 C_(Mn), ppb 200 420 0.9 1

As can be seen, the acid and salt treatments together essentially greatly reduced the presence of manganese in the peat granule to free up active sorption sites, while also serving to eliminate the leaching of manganese into the aqueous solution, which can be undesirable for some wastewater treatment end uses. At the same time, the cadmium adsorption of the acid/salt-treated media indicates much higher sorption activity, particularly for cadmium, compared with the parent peat material and the APTsorb II material.

The first step, an acid treatment step, effectively removed the greater part of the mineral form of manganese and other contaminants, and likely also displaced some of the ions that are filling ion-exchange sites with hydrogen. The second step, a salt treatment step, regenerated the other active sites besides ion-exchange on the media to a sodium form. Sodium, which is a single-valent cation, is not the preferred ion for those sites, but the equilibrium of the process is driven by concentration and heat to the sodium-form state. Therefore, when the media is subjected to a target metal, competing ions with a valence of +2 readily displace the sodium ions, which makes the media more active towards sorption of metals compared with the parent material.

The result of this mechanism is illustrated in Table 4, where the concentration of manganese leaching into the solution is reduced from 420 ppb for the APTsorb II material to 1 ppb for the APTsorb III product. Simultaneously, the cadmium sorption activity of the APTsorb III product is enhanced over the APTsorb II material, and even the parent peat material. The APTsorb III product left between 50 and 160 ppb cadmium in solution, versus 1200 and 1400 ppb for raw peat and the APTsorb II material, respectively. Thus, the APTsorb III product seems to provide highly beneficial cation metal adsorption characteristics.

Example 4—Activity of APTsorb III Peat Granules for Adsorption of Heavy Metals

The equilibrium test was performed using APTsorb II material and the APTsorb III product with other metal ions in order to determine their respective affinities for heavy metals other than cadmium, and to compare the performance gains of the APTsorb III product over the APTsorb II material. The typical test procedure uses 1 g of APTsorb II or APTsorb III peat granules dried at 105° C. for 24 hrs, which was added to 100 ml of a solution of metal ion in Type I deionized water. The mixture was tumbled in an end-over-end fashion at 8-28 rpm at room temperature (20±2° C.) in a leak-proof vessel for 24 hrs. The mixture was filtered using 0.45 μm polypropylene filter membrane, and the filtrate was preserved by adding of a solution of HNO₃. The initial and final concentrations of metal ions were measured by graphite furnace atomic adsorption spectrophotometry. The results are shown in Table 5 and FIG. 4.

TABLE 5 Comparison of adsorption activity of APTsorb II and APTsorb III granular peat products. Metal ions Co²⁺ Cu²⁺ Ni²⁺ Zn²⁺ Cd²⁺ Pb²⁺ C_(initial), ppb 29000 22000 23000 32000 30000 51,000 APTsorb II peat granules C_(final), ppb 2100 1300 1900 1400 960 980 Percent of 87.65 87.65 92.78 82.73 92.22 96.16 removal (%) APTsorb III peat granules C_(final), ppb 360 500 420 300 50 380 Percent of 98.76 97.73 98.17 99.06 99.83 99.25 removal (%) In all cases, the adsorption activity for metal cations of the APTsorb III peat product was dramatically improved compared with the APTsorb II starting material. These results demonstrate that the chemical treatment of peat media increases the activity of the surface chemistry of the peat granules, thereby resulting in a more active adsorption media for heavy metal adsorption. They also demonstrate once again the highly beneficial cation metal adsorption characteristics of the APTsorb III product.

Example 5—Determining the Adsorption Capacity for Cadmium by an APTsorb III Sorption Medium Used in a One Metal Cation Aqueous Environment

The experimental set-up for the column system consisted of a plastic column resulting in a bed size of 62 mm in diameter and 50 mm deep and a bed volume of 150.95 cm³. 72.3 g of APTsorb III sorption medium prepared in accordance with Example 3 and then loaded with sodium cations on its active sites, and having a particle size distribution of between 10-50 mesh, were submerged in type I deionized water (18.2 MOhm) for 10 hours to wet the surface of the granules and allow the granules to swell. Plastic mesh was installed at both the top and the bottom of the column. The column was packed with 20 mm of HCl-washed Red Flint filter gravel (granular size 3-5 mm) sourced from Red Flint Rock and Stone of Eau Claire, Wis., and then with 50 mm of the pre-wetted APTsorb III granules.

A synthetic solution of cadmium with a concentration 6 ppm was prepared by dissolving cadmium chloride in Type I deionized water (18.2 MOhm).

Five bed volumes of type I deionized water were pumped through the column containing the APTsorb III granules prior to the testing solution. A solution of 6 mg/L cadmium in water was then pumped from a holding tank to the bottom of the column (up-flow, fixed-bed). The liquid flow rate was controlled by a peristaltic pump. All experiments were performed at 25° C. and at an initial pH of 5.7. In order to ensure the formation of a complete breakthrough curve, water samples were collected using a Foxy 200 fraction collector. In the event that air started to accumulate in the column, the air was either forced out by tapping the column walls or the top of the column was removed.

Each water sample was preserved by addition of a solution of HNO₃ (TraceMetal Grade) in water and analyzed for the concentration of Cd²⁺ using a flame ionization or a graphite furnace atomic absorption spectroscopy technique and Zn²⁺ using flame ionization atomic absorption spectroscopy technique. Breakthrough behavior was evaluated by plotting the cadmium concentration in the effluent as a function of the total number of bed volumes that had been treated. The amount of metal ion adsorbed in the column was determined from the area above the breakthrough curve assuming the breakthrough happens when the concentration of the metal in the effluent reaches 50 ppb. The absorption capacity of the chemically-treated APTsorb III granules was verified by digesting the spent granules and measuring the concentration of the metal ions.

Employing a flow rate for the cadmium aqueous solution of 1.99 BV/hr and a contact time of 30.19 minutes, the breakthrough capacity for adsorption of cadmium at breakthrough concentration 50 ppb was found to be 16.43 mg/g at 0.1 m/hr flow velocity. “Breakthrough capacity” measures the effective total loading of the peat adsorption sites with cadmium when the column effluent concentration climbs to 50 ppb cadmium. The data for this experiment is shown in Table 6 and FIG. 5.

TABLE 6 Cd feed Flow Column Bed Bed Flow Flow Contact Number Breakthrough grade, rate, m_(granules), diameter, depth, volume, rate, velocity, time, of treat- capacity at Granules ppm ml/min g cm cm cm³ BV/hr m/hr min ed BV 50 ppb, mg/g APTsorb III 6 5 72 6.2 5 150.95 1.99 0.10 30.19 1306 16.43 With waste waters containing high concentrations of cadmium and no other types of metal cations present, there is a coefficient that will define this equilibrium adsorption by the peat granules for Cd²⁺. This ultimately controls the 16.43 mg/g breakthrough capacity value for the APTsorb III peat granules within the aqueous solution environment containing cadmium metal cations alone. Once again, this experiment supports the notion that the APTsorb III granule medium is highly beneficial for cadmium adsorption in wastewater treatments.

Example 6—Determining the Adsorption Capacity for Cadmium by an APTsorb III Sorption Medium in the Presence of Zinc within a Competing Metal Cation Environment

But, if the aqueous solution contains a second metal cation like zinc (Zn²⁺), which frequently occurs in waste waters, then the presence of the Zn²⁺ cations will retard the adsorption capacity of the peat granule sorption medium for the Cd²⁺ cations. Because the Zn²⁺ cations usually appear in the wastewater solution at higher concentrations than the Cd²⁺ cations, the Zn²⁺ cations occupy many of the active sites on the peat granules to the exclusion of Cd²⁺ adsorption.

Using the Column Procedure described above (Example 5), a synthetic solution of cadmium and zinc with concentrations 4.59 ppm cadmium and 29.3 ppm zinc was prepared by dissolving cadmium chloride and zinc sulfate in Type I deionized water (18.2 MOhm). APTsorb III peat granules were loaded into the column having a column diameter of 62 mm, a bed depth of 5 cm, and a bed volume of 151 cm³. Employing a flow rate for the cadmium/zinc aqueous solution of 1.99 BV/hr, the breakthrough capacity for adsorption of cadmium at breakthrough concentration 50 ppb was found to be only 0.47 mg/g at 0.1 m/hr flow velocity. The data for this experiment is shown in Table 7 and FIG. 6. This demonstrates the unwanted competition by the zinc cations for the active sites on the APTsorb III peat granules to the exclusion of cadmium adsorption during the treatment process, which resulted in the breakthrough capacity for the APTsorb III peat granule sorption medium falling from the 16.43 mg/g value shown in Example 5 for the cadmium single metal cation aqueous solution environment to 0.47 mg/g in this Example 6 for the two metal cation environment. This represents a problem for the treatment of aqueous solutions using the APTsorb III granules to remove the Cd²⁺ cations where Zn²⁺ cations are present within the aqueous solution.

TABLE 7 Zn feed Cd feed Flow Column Bed Bed Flow Flow Cd breakthrough grade, grade, rate, m_(granules), diameter, depth, volume, rate, velocity, capacity at ppm ppm ml/min g cm cm cm³ BV/h m/h 50 ppb, mg/g 29.3 4.59 5 72 6.2 5.00 151 1.99 0.1 0.47

Example 7—Determining the Selectivity, Activity, and Distribution Coefficient for Cadmium by a APTsorb II*M Sorption Medium in the Presence of Zinc within a Competing Metal Cation Environment

Preparation of the APTsorb II*M Medium

Because of the poor performance by the APTsorb III peat granule medium, as exemplified by Example 6 using the APTsorb III medium, for selective adsorption of cadmium cations over zinc cations within a competing metals aqueous solution environment, the research focus was changed to metal cation-loaded APTsorb II peat granules (APTsorb II*M). This was done despite the fact that the cadmium adsorption activity for the APTsorb II peat granules is much lower than the cadmium adsorption activity for the APTsorb III granules.

APTsorb II*Na peat granule medium was prepared as follows: 500 g of APTsorb II granules prepared in accordance with the method set forth in Example 2 was added to 2.5 L of 1 M NaCl solution. The resulting mixture was refluxed by placing it on a hot plate and gently boiled for 90 minutes at a temperature around 100° C. This mixture was then filtered while still hot using a Buchner funnel under vacuum to remove the solution. The filtrate media was then rinsed with 3 L of hot D.I. water. The resulting rinsed media was then rinsed with 4-6 L of room temperature D.I. water until the filtrate was free of chloride ions using the “silver nitrate test.” This test was administered to indicate the presence of chloride ions by adding 0.5 ml of a 1% solution of silver nitrate to a 20 ml sample of rinsing water. If chlorides were present, a white precipitate in the form of silver chloride formed immediately and evidenced the need for additional rinsing. The rinsed medium was dried at 105° C. for 24 hours to obtain the final APTsorb II*Na peat granule product.

Samples of other forms of APTsorb II*M peat granule medium were prepared by the method described above, using the following metal solutions:

-   -   LiCl to produce APTsorb II*Li peat granule medium.     -   KCl to produce APTsorb II*K peat granule medium.     -   NH₄Cl to produce APTsorb II*NH₄ peat granule medium.     -   CaCl₂ to produce APTsorb II*Ca peat granule medium.     -   MgCl₂ to produce APTsorb II*Mg peat granule medium.     -   BaCl₂ to produce APTsorb II*Ba peat granule medium.     -   MnCl₂ to produce APTsorb II*Mn peat granule medium.     -   FeCl₂ to produce APTsorb II*Fe(II) peat granule medium.     -   Al₂(SO₄)₃ to produce APTsorb II*Al peat granule medium.     -   Fe₂(SO₄)₃ to produce APTsorb II*Fe(III) peat granule medium.         For non-chloride metal solutions, a barium chloride solution         test was employed instead of the silver nitrate solution to test         for the presence of SO₄ ²⁻ ions during the rinse steps.         Preparation of the APTsorb II-HCl*M Peat Medium

A set of acid and metal salt-treated derivatives of the APTsorb II*M medium described above (APTsorb II-HCl*M) were prepared as follows: 500 g of APTsorb II was added to 1 L of a 1 N solution of HCl in type I D.I. water. The mixture was kept at room temperature for 24 hours with periodic shaking so as not to destroy the granules. After the acid treatment, the media was rinsed with deionized water until the filtrate was free of chlorides as described in the test above. The media was then mixed with 2.5 L of 1 M NaCl solution and heated. The mixture was held at 90-100° C. for 90 minutes, filtered while still hot, and rinsed until free of chlorides as described above. The treated media was then dried for 24 h at 105° C. to give APTsorb II-HCl*Na peat granular media. Samples of other forms of APTsorb II-HCl*M peat granule medium were prepared by the method described above.

Preparation of the APTsorb III*M Peat Medium

The production of APTsorb III was described in Example 2. APTsorb III*Na granules were prepared using the following procedure: 500 g of APTsorb III granules prepared in accordance with the method set forth in Example 2 was added to 2.5 L of 1 M NaCl solution. The resulting mixture was refluxed by placing it on a hot plate and gently boiled for 90 minutes at a temperature around 100° C. This mixture was then filtered while still hot using a Buchner funnel under vacuum to remove the solution. The filtrate media was then rinsed with 3 L of hot D.I. water. The resulting rinsed media was then rinsed with 4-6 L of room temperature D.I. water until the filtrate was free of chloride ions using the “silver nitrate test.”

Other samples of APTsorb III*Li medium, APTsorb III*K medium, APTsorb III*NH₄ medium, APTsorb III*Ca medium, APTsorb III*Mg medium, APTsorb III*Ba medium, APTsorb III*Mn medium, APTsorb III*Fe(II) medium, APTsorb III*Al medium, and APTsorb III*Fe(III) medium were prepared using this method in conjunction with the metal solutions described above.

Adsorption Activity by Cadmium Equilibrium Test

The cadmium adsorption exhibited by the different media was measured using a Cadmium Equilibrium Test as follows: 1 g of dried media was added to 100 ml of a 30 ppm solution of Cd²⁺ in type I D.I. water. The mixture was rolled at 8 rpm at room temperature in a leak-proof vessel for 24 hours. The solution was filtered using 0.45 μm polypropylene syringe membrane filter. The filtered solution was preserved by concentrated HNO₃ (TraceMetal Grade) and analyzed by flame spectroscopy or graphite furnace atomic absorption spectroscopy for the concentration of Cd²⁺ ion. This procedure measures the activity of the media toward sorption of Cd²⁺ cations. A lower concentration of Cd²⁺ in the solution translates into more of the Cd²⁺ being adsorbed onto the media and thereby indicates greater activity. Cadmium adsorption data for the different derivatives of APTsorb II*M, APTsorb II-HCl*M, and APTsorb III*M samples are presented in Table 8 and FIG. 10. These data represent the activity of the sample toward sorption of cadmium. The lower the remaining concentration of Cd²⁺ contained in the solution represents the higher activity of the peat granule sample. The most active samples are APTsorb III*M, where M is an alkaline metal.

Adsorption Activity of Peat Granules by Zinc Equilibrium Test

The zinc adsorption exhibited by the different media was measured using a Zinc Equilibrium Test as follows: 1 g of dried media was added to 100 ml of a 30 ppm solution of Zn²⁺ in type I D.I. water. The mixture was rolled at 8 rpm at room temperature in a leak-proof vessel for 24 hours. The mixture was filtered using 0.45 μm polypropylene syringe membrane filter. The filtered solution was preserved by concentrated HNO₃ (TraceMetal Grade) and analyzed by flame spectroscopy or graphite furnace atomic absorption spectroscopy for the concentration of Zn²⁺ ion. This procedure measures the activity of the media toward sorption Zn²⁺ cations. A lower concentration of Zn²⁺ in the solution translates into more of the Zn² being adsorbed onto the media and thereby indicates greater activity. Zinc adsorption data for the different derivatives of APTsorb II*M, APTsorb II-HCl*M, and APTsorb III*M samples are presented in Table 8. These data represent the activity of the sample toward sorption of zinc. The lower the remaining concentration of Zn²⁺ in the solution represents the higher activity of peat sample. The most active samples are APTsorb III*M, where M is an alkaline metal.

Selectivity for Sorption of Cadmium in the Presence of Zinc Cation

The selectivity for cadmium cations over zinc cations and the distribution coefficients for the various samples were measured as follows: 1 g of dried peat media was added to 100 ml of a 30 ppm solution of Zn²⁺ and 30 ppm solution of Cd²⁺ in type I D.I. water. The mixture was rolled at 8 rpm at room temperature in a leak-proof vessel for 24 hours. The mixture was filtered using 0.45 μm polypropylene syringe membrane filter. The solution was preserved by adding a concentrated HNO₃ (TraceMetal Grade) and analyzed by flame spectroscopy or graphite furnace atomic absorption spectroscopy for the concentration of Zn²⁺ and Cd²⁺ ions. This procedure measures the final concentration of Zn²⁺ and Cd²⁺ ions contained in the solution. The zinc and cadmium adsorption equilibrium test results in the competing metals aqueous solution environment for the different APTsorb II*M, APTsorb II-HCl*M, and APTsorb III*M samples are presented in Table 8.

The distribution coefficient of Zn²⁺ cation was calculated using the following formula:

C_(Zn solid)—concentration of Zn²⁺ ions, which was sorbed on the peat granules, mmol/g. C_(Zn solution)—concentration of Zn²⁺ ions in a solution after equilibrium, mmol/L.

The distribution coefficient of Cd²⁺ cation was calculated using the following formula:

$\lambda_{Cd} = \frac{C_{{Cd}\mspace{20mu}{solid}}}{C_{{Cd}\mspace{14mu}{solution}}}$ C_(Cd solid)—concentration of Cd²⁺ ions, which was sorbed on the peat granules, mmol/g. C_(Cd solution)—concentration of Cd²⁺ ions in a solution after equilibrium, mmol/L.

Next, the selectivity values for Cd²⁺ ions over Zn²⁺ ions for the various samples were calculated as follows:

λ_(Cd)—distribution coefficient of Cd²⁺ cation λ_(Zn)—distribution coefficient of Zn²⁺ cation. The distribution coefficient and selectivity of cadmium ions over zinc ions in the competing metals aqueous solution environment for the different APTsorb II*M, PTsorb II-HCl*M, and APTsorb III*M samples are presented in Table 8 and FIGS. 7-10.

TABLE 8 Sorption activity, distribution coefficient, and selectivity for different peat media. Remaining concentration of Zn and Cd ions in the solution Distribution Zn Equilib Cd Equilib Zn and Cd Equilib coefficient λ Selectivity, Test Test Test (mmol/kg)/(mmol/L) α Media Ion Zn, ppm Cd, ppm Zn, ppm Cd, ppm Zn Cd Cd/Zn APTsorb II*HCl 9.11 4.5 12.9 10.61 138 205 1.49 APTsorb II 1.76 0.95 1.54 1.02 1,894 3,076 1.62 APTsorb III 0.299 0.1 0.766 0.6432 3,908 4,937 1.26 Raw Peat 0.784 0.4294 1.33 0.848 2,208 3,721 1.68 Derivatives of APTsorb II peat media APTsorb II STRT 1.76 0.95 1.54 1.02 1,894 3,076 1.62 APTsorb II*Li Li⁺ 0.3565 0.202 0.387 0.209 7,938 15,093 1.90 APTsorb II*Na Na⁺ 0.657 0.278 0.742 0.284 4,066 10,748 2.65 APTsorb II*K K⁺ 0.391 0.199 0.434 0.226 7,073 13,953 1.97 APTsorb II*NH₄ NH₄ ⁺ 0.439 0.224 0.563 0.356 5,424 8,794 1.62 APTsorb II*Ca Ca²⁺ 1.170 0.883 1.446 0.597 2,106 5,027 2.39 APTsorb II*Mg Mg²⁺ 0.637 0.304 0.666 0.373 4,690 8,098 1.73 APTsorb II*Ba Ba²⁺ 0.919 0.513 2.060 0.659 1,623 3,906 2.41 APTsorb II*Mn Mn²⁺ 1.444 0.705 1.742 0.974 1,579 2,884 1.83 APTsorb II*Fe(II) Fe²⁺ 6.060 1.100 9.150 5.635 288.0 368.7 1.28 APTsorb II*Al Al³⁺ 18.720 12.720 21.000 19.480 39.3 49.2 1.25 APTsorb II*Fe(III) Fe³⁺ 17.500 13.290 20.050 14.010 56.1 111.9 1.99 Derivatives of APTsorb II HCl peat media APTsorb II*HCl STRT 9.11 4.5 12.9 10.61 138 205 1.49 APTsorb II HCl*Li Li⁺ 0.411 0.1151 3.305 2.7495 841 1,054 1.25 APTsorb II HCl*Na Na⁺ 0.299 0.1 0.766 0.6432 3,908 4,937 1.26 APTsorb II HCl*K K⁺ 0.46 0.12 2.21 1.79 1,285 1,634 1.27 APTsorb II HCl*NH₄ NH₄ ⁺ 0.419 0.1057 2.88 2.183 980 1,351 1.38 APTsorb II HCl*Ca Ca²⁺ 7.52 4.151 10.31 7.826 209.4 291.1 1.39 APTsorb II HCl*Mg Mg²⁺ 4.23 2.499 6.95 8.212 359.0 272.7 0.76 APTsorb II HCl*Ba Ba²⁺ 3.29 4.57 7.78 5.158 299.7 514.2 1.72 APTsorb II HCl*Mn Mn²⁺ 4.84 2.644 7 6.462 317.9 349.7 1.10 APTsorb II HCl*Fe(II) Fe²⁺ 11.65 5.75 15.2 12.8 133.6 106.3 0.80 APTsorb II HCl*Fe(III) Al³⁺ 17.7 23.24 17.9 15.065 74.9 97.1 1.30 APTsorb II HCl*Al Fe³⁺ 14.5 9.98 18.24 17.24 60.4 68.6 1.14 Derivatives of APTsorb III peat media APTsorb III STRT 0.299 0.1 0.766 0.6432 3,908 4,937 1.26 APTsorb III*Li Li⁺ 0.091 0.048 0.130 0.083 23,919 38,299 1.60 APTsorb III*Na Na⁺ 0.199 0.108 0.322 0.133 10,925 19,817 1.81 APTsorb III*K K⁺ 0.133 0.048 0.318 0.194 10,031 16,047 1.64 APTsorb III*NH₄ NH₄ ⁺ 0.145 0.044 0.799 0.608 3,792 5,111 1.35 APTsorb III*Ca Ca²⁺ 6.23 3.079 9.010 7.810 254.1 291.9 1.15 APTsorb III*Mg Mg²⁺ 2.74 0.964 4.370 3.116 630.0 882.3 1.40 APTsorb III*Ba Ba²⁺ 2.96 2.589 6.400 3.309 385.9 857.4 2.22 APTsorb III*Mn Mn²⁺ 4.1 2.148 6.560 5.459 345.9 432.3 1.25 APTsorb III*Fe(II) Fe²⁺ 13.4 4.902 15.400 12.250 130.5 115.6 0.89 APTsorb III*Al Al³⁺ 17.94 12.990 19.160 21.685 52.7 34.0 0.65 APTsorb III*Fe(III) Fe³⁺ 15.9 9.786 18.350 15.090 70.6 96.8 1.37

As can be seen from the data in Table 8, the APTsorb II medium without metal cation loading exhibits greater adsorption selectivity (1.62) for cadmium over zinc cations within a competing metals cation aqueous solution environment, compared with the APTsorb III medium (1.26). But, this selectivity value also remains essentially unchanged from the selectivity exhibited by the raw peat starting material (1.68). By resorting instead to a metal cation-loaded derivative of APTsorb II medium (i.e., APTsorb II*M), the selectivity results are improved, particularly for the alkaline metal (+1) derivatives. This is particularly true for APTsorb II*Na medium having a selectivity value of 2.65, which represents an average of several experimental results. A selectivity value of 3.00 was also obtained for the APTsorb II*M medium. See also APTsorb II*Li (1.90) and APTsorb II*K (1.97). The selectivity values for the alkaline earth metal (+2) derivatives also look beneficial. See APTsorb II*Ca (2.39), APTsorb II*Mg (1.73), APTsorb II*Ba (2.41), APTsorb II*Mn (1.83), APTsorb II*Li (1.90), and APTsorb II*Fe(III) (1.99). Meanwhile, the selectivity values for these APTsorb II*M derivatives is greater than the APTsorb III*M derivatives. The acid treatment applied to the APTsorb II-HCl*M derivatives seems to have harmed the selectivity property for those media. This may be due to the fact that the HCl acid reacted with the calcium carbonate contained in the APTsorb II starting material. Therefore, calcium carbonate along with metal plays a key role in increasing the selectivity.

The sorption activity for Cd²⁺ is decreasing with an increase of charge of the metal: APTsorb II*M⁺>APTsorb II*M²⁺>APTsorb II*M³⁺ or APTsorb II*Na⁺ (0.657)>Raw peat (0.784)>APTsorb II*Ca²⁺ (1.17)>APTsorb II*Fe³⁺ (17.5). This trend indicates the importance for the alkaline metal (+1) derivatives. The highest activity was found in the APTsorb III*M⁺ samples (APTsorb III*Li⁺—0.091), however, the selectivity values for these samples drops dramatically.

Note that these adsorption activity values actually represent measurements of the cadmium concentration in the effluent aqueous solution. Thus, a higher value means that more of the cadmium cations in the influent aqueous solution remained in the solution and were not adsorbed onto the APTsorb II*M granules. Conversely, a lower value means that less of the cadmium cations in the influent aqueous solution remained in the solution and were adsorbed instead onto the APTsorb II*M granules—i.e., a high adsorption activity for the medium. Hence, a lower value is better.

Example 8—Determining the Breakthrough Capacity for Cadmium by an APTsorb II, APTsorb II*Na, APTsorb II*Zn, and APTsorb III*Na Sorption Medium in the Presence of Zinc within a Competing Metal Cation Environment

APTsorb II, APTsorb II*Na, APTsorb III, and APTsorb III*Na were chosen as the most selective or the most active peat granular media according to the equilibrium tests. Since it was not possible to derive a selectivity coefficient for APTsorb II*Zn peat media using equilibrium test, the column test was the next choice. The experimental setup for the column system consisted of a plastic column resulting in a bed size of 62 mm in diameter and approximately 50 mm deep, depending upon the wet density of peat media. The wet density of each media was measured separately. 72 g of peat material (particle size distribution between 10-50 mesh) were submerged in type I D.I. water (18.2 MOhm) for 10 hours to wet the surface of the granules and allow the granules to swell. Plastic mesh was installed at both the top and the bottom of the column. The column was packed with 20 mm of HCl-washed Red Flint filter gravel (granular size 3-5 mm) sourced from Red Flint Rock and Stone of Eau Claire, Wis., and then with 72 g of pre-wetted peat media. Five bed volumes of type I D.I. water were pumped through the column prior to the testing solution. A solution of 5 ppm cadmium and 30 ppm zinc in type I DI water was then pumped from a holding tank to the bottom of the column (up-flow, fixed-bed). The liquid flow rate was controlled by a peristaltic pump. All experiments were performed at 25° C. and at an initial pH of 5.7.

In order to ensure the formation of a complete breakthrough curve, water samples were collected using a Foxy 200 fraction collector. Each water sample was preserved by addition of a solution of HNO₃ (TraceMetal Grade) in water and analyzed for the concentration of Zn^(2±) and Cd²⁺ ions using a flame spectroscopy or graphite furnace atomic absorption spectroscopy technique. Breakthrough behavior was evaluated by plotting the cadmium and zinc solution concentrations in the effluent as a function of the total number of bed volumes that had been treated. The amount of cadmium ion adsorbed in the column was determined from the area above the breakthrough curve assuming the breakthrough happens when the concentration of cadmium in the effluent reaches 50 ppb. The absorption capacity of the modified APTsorb granules was verified by digesting the spent granules and measuring the concentration of Cd²⁺ and Zn²⁺. The breakthrough sorption capacity of the peat media was measured at two flow velocities of influent: 0.1 m/hr and 0.4 m/hr. Column data is presented in Table 9 and FIGS. 11-12.

TABLE 9 Cadmium breakthrough capacity using column test. Break- through C_(Zn) when Column Flow capacity C_(Cd) = 50 Feed grade Flow diam- Bed Bed Flow veloc- Cd at ppb in Column Zn Cd rate, m_(granules), eter, depth, Area, volume, rate, ity, 50 ppb, effluent, # Media ppm ppm ml/min g cm cm cm² cm³ BV/h m/h BV mg/g ppm 1 APTsorb II 30.0 4.81 5 72 6.2 5.00 30.19 151 1.99 0.10 261.00 2.63 >1.4 2 APTsorb II 32.1 7.42 20 72 6.2 5.00 30.19 151 7.95 0.40 88.00 1.37 3 APTsorb III 29.3 4.59 5 72 6.2 5.00 30.19 151 1.99 0.10 49.00 0.47 0.92 4 APTsorb II*Na 29.4 5.63 5 72 6.2 5.50 30.19 166 1.81 0.10 230.00 2.99 1.64 5 APTsorb II*Na 30.4 4.44 5 72 6.2 5.50 30.19 166 1.81 0.10 297.00 3.04 3 6 APTsorb II*Na 29.6 4.68 20 72 6.2 5.50 30.19 166 7.23 0.40 194.00 2.09 1.3 7 APTsorb II*Zn 31.2 6.13 5 72 6.2 5.00 30.19 151 1.99 0.10 130.00 1.67 34 8 APTsorb II*Zn 32.6 6.1 20 72 6.2 5.00 30.19 151 7.95 0.40 55.00 0.70 34

APTsorb II*Na peat granular media exhibits the highest breakthrough capacity for cadmium cations in the column test, around 3.04 mg/g, which suggests that the equilibrium test is a suitable technique to measure the selectivity of cadmium sorption in the presence of zinc. APTsorb III peat granules have the highest activity to sorb cadmium with lowest selectivity and, therefore, lowest breakthrough capacity—0.47 mg/g. APTsorb II peat media showed a higher capacity for sorption of cadmium ion (2.63 mg/g) compare to APTsorb III media. However, increasing the flow velocity from 0.1 m/h to 0.4 m/h decreases the sorption capacity 2 times (from 2.63 mg/g to 1.37 mg/g) for APTsorb II. Treating APTsorb II with Na⁺ ion produces a product, APTsorb II*Na, which exhibits the highest breakthrough capacity (3.04 mg/g) and increasing the flow velocity from 0.1 m/h to 0.4 m/h decreases the sorption capacity only 1.5 times (from 3.04 mg/g to 2.09 mg/g), thereby suggesting the importance of treatment with Na⁺ ion. Therefore, the addition of CaCO₃ to the raw peat, thermally activating the resulting granules, and chemically treating the resulting thermally-activated granules with Na⁺ ion produces a product that exhibits the highest selectivity to sorb cadmium in the presence of zinc ions.

The above specification, drawings, examples, and data provide a complete description of the thermally-activated, chemically-treated sorption media and associated preparation method of the present invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. 

We claim:
 1. A process for the production from partially decomposed organic matter of a sorption media for use in the treatment of aqueous solutions comprising at least one more-toxic metal and at least one less-toxic metal to remove at least one type of aqueous contaminant therein, comprising the steps of: (a) supplying an amount of the partially decomposed moisture-bearing organic matter to a granulating machine; (b) granulating the partially decomposed organic matter after introducing a synergistic interactive agent; (c) drying the granules; (d) thermally activating the granules without chemical activation using an activation heat medium at a temperature of about 175-287° C., wherein the granule has a Ball-Pan Hardness number of about 75%-400% and is suitable for sorption of the aqueous contaminant found in the aqueous solution; and (e) chemically treating the thermally-activated granule with a salt solution preselected in the form of a soluble salt compound having a cation constituent and an anion constituent, wherein: (i) the cation constituent of the salt solution is selected from the group consisting of any 1⁺ or 2⁺ cation of, without limitation, ammonium (NH₄ ⁺), ammonium groups (NR₄ ⁺), sodium, potassium, lithium, cesium, beryllium, magnesium, calcium, barium, manganese, copper, zinc, strontium, and iron; (ii) the anion constituent of the salt solution is selected from the group consisting of SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, NO₃ ⁻, NO₂ ⁻, PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, Cl⁻, I⁻, Br⁻, F⁻, HCOO⁻, CH₃COO⁻, C₂H₅COO⁻, C₃H₇COO⁻, C₄H₉COO⁻, ClO₄ ⁻, HCO₃ ⁻, or CO₃ ²⁻; (iii) the chemical treatment of the granule with the salt solution places the selected cations provided by the cation constituent of the salt solution onto the active adsorption sites in the granule; (f) wherein the presence of the cations of the cation constituent of the salt solution on the active sites of the granule interacts with the synergistic interactive agent to alter the coefficient that defines the solution equilibrium of the aqueous solution to influence the adsorption capacity of the thermally-activated and chemically-treated sorption medium granules to selectively adsorb the more-toxic metal cations at the expense of the less-toxic metal contaminant cations, and increase the adsorption activity of the granules for the more-toxic metal cations, so that the granules can sorb the more-toxic metal cations from the treated aqueous solution, while leaving a substantial portion of the less-toxic metal contaminant cations in the aqueous solution.
 2. The process of claim 1, wherein the synergistic interactive agent is calcium carbonate or another alkaline earth metal carbonate compound.
 3. The process of claim 1, wherein the synergistic interactive agent is a non-water soluble salt made out of anions of polyprotic acids selected from the group consisting of PO₄ ³⁻, HPO₄ ²⁻, H₂PO4⁻, SO₄ ²⁻, HSO₄ ⁻, C₂O₄ ²⁻ (oxalic acid), HC₂O₄ ⁻, C₆H₈O₄ ²⁻ (adipic acid), C₆H₉O₄ ⁻ (adipic acid), C₆H₄(COO)₂ ²⁻ (phthalic acid), and C₆H₄C₂O₄H⁻, and cations of an alkaline earth metal cations selected from the group consisting of Ca²⁺, Mg²⁺, Be²⁺, Ba²⁺, and Sr²⁺.
 4. The process of claim 1, wherein for an aqueous solution containing cadmium as the more-toxic metal cations and zinc as the less-toxic metal cations, the selectivity of the granule for the cadmium cations over the zinc cations is 1.62<α≤3.00 when the initial influent concentration is C_(Cd)=30 ppm and C_(Zn)=30 ppm.
 5. The process of claim 1, wherein for an aqueous solution containing cadmium as the more-toxic metal cations and zinc as the less-toxic metal cations, the cadmium adsorption activity of the granule, as measured by cadmium concentration in the aqueous solution, is 1.02 ppm<C_(Cd)≤0.209 ppm when the initial influent concentration is C_(Cd)=30 ppm and C_(Zn)=30 ppm.
 6. The process of claim 1, wherein for an aqueous solution containing cadmium as the more-toxic metal cations and zinc as the less-toxic metal cations, the zinc adsorption activity of the granule, as measured by zinc concentration in the aqueous solution, is 1.54 ppm<CZn≤0.387 ppm when the initial influent concentration is C_(Cd)=30 ppm and C_(Zn)=30 ppm.
 7. The process of claim 1, wherein the granule used within an aqueous solution treatment further comprises a greater breakthrough capacity for the more-toxic metal cations.
 8. The process of claim 7, wherein for an aqueous solution containing cadmium as the more-toxic metal cations and zinc as the less-toxic metal cations, the breakthrough capacity for cadmium cations of the granule is 2.99-3.04 mg/g Cd at 50 ppb at 0.1 m/hr flow velocity when the initial influent concentration is C_(Cd)=30 ppm and C_(Zn)=30 ppm.
 9. The process of claim 7, wherein the pre-selected soluble salt compound for the salt solution used in the chemical treatment step for the production of the sorption medium results in an improved breakthrough capacity for the more-toxic metal contaminant up to 21.32 mg/g at 50 ppb of the major toxic metal.
 10. The process of claim 1, wherein the more-toxic metal contaminant found in the aqueous solution is selected from the group consisting of a chemical element or compound that poses a health risk to humans or animals, or is otherwise subject to environmental laws or regulations in the form of heavy metals comprising arsenic, lead, mercury, cadmium, manganese, iron, nickel, copper, molybdenum, cobalt, chromium, palladium, stannum, or aluminum; radioactive materials like cesium or various isotopes of uranium; selenium and boron.
 11. The process of claim 1, wherein the less-toxic metal contaminant found in the aqueous solution is selected from the group consisting of a chemical element or compound found in an aqueous solution that does not necessarily pose a health risk to humans or animals or is otherwise subject to environmental laws or regulations in the form of metals comprising magnesium, beryllium, strontium, barium, calcium, manganese, copper, zinc, iron, potassium, lithium, ammonium, and ammonium groups.
 12. The process of claim 1, wherein the partially decomposed organic matter is selected from the group consisting of compost media, livestock manure, sewage sludge, and combinations thereof.
 13. The process of claim 12, wherein the partially decomposed organic matter is compost media.
 14. The process of claim 13, wherein the compost media is selected from the group consisting of leaf compost media, peat, plant by-products, and combinations thereof.
 15. The process of claim 1, wherein the aqueous solution comprises a water-based solution containing an environmental impurity as a solute produced by manufacturing, agricultural, or mining industries, or population communities.
 16. The process of claim 1, wherein the granule temperature during the drying step is conducted at a temperature of about 80-400° C.
 17. The process of claim 16, wherein the moisture level of peat granules is reduced within the drying step from about 40% wt. to about 10-14% wt.
 18. The process of claim 1, wherein the granules are thermally activated in an inert environment.
 19. The process of claim 1 wherein the activation heat medium comprises steam or carbon dioxide, nitrogen or other inert media, or combinations thereof at a temperature of about 175-287° C. until the desired level of hardness and activation is achieved.
 20. The process of claim 1, wherein the thermal activation step for the granule is carried out at a temperature of about 200-275° C.
 21. The process of claim 1, wherein the granule has a Ball-Pan Hardness of about 80-98%.
 22. A process for the production of a chemically-treated sorption media made from partially decomposed organic matter for use in the treatment of aqueous solutions comprising at least one more-toxic metal and at least one less-toxic metal to remove at least one type of aqueous contaminant therein, comprising the steps of: (a) supplying an amount of a thermally-activated, granulated, partially-decomposed moisture-bearing organic matter that was not chemically activated and contains a synergistic interactive agent; (b) chemically treating the thermally-activated granule with a salt solution preselected in the form of a soluble salt compound having a cation constituent and an anion constituent, wherein: (i) the cation constituent of the salt solution is selected from the group consisting of any 1⁺ or 2⁺ cation of, without limitation, ammonium (NH₄ ⁺), ammonium groups (NR₄ ⁺), sodium, potassium, lithium, cesium, beryllium, magnesium, calcium, barium, manganese, copper, zinc, strontium, and iron; (ii) the anion constituent of the salt solution is selected from the group consisting of SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, NO₃ ⁻, NO₂ ⁻, PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, Cl⁻, I⁻, Br⁻, F⁻, HCOO⁻, CH₃COO⁻, C₂H₅COO⁻, C₃H₇COO⁻, C₄H₉COO⁻, ClO₄ ⁻, HCO₃ ⁻, or CO₃ ²⁻; (iii) the chemical treatment of the granule with the salt solution places the selected cations provided by the cation constituent of the salt solution onto the active adsorption sites in the granule; (c) wherein the presence of the cations of the cation constituent of the salt solution on the active sites of the granule interacts with the synergistic interactive agent to alter the coefficient that defines the solution equilibrium of the aqueous solution to influence the adsorption capacity of the thermally-activated and chemically-treated sorption medium granules to selectively adsorb the more-toxic metal cations at the expense of the less-toxic metal contaminant cations, and increase the adsorption activity of the granules for the more-toxic metal cations, so that the granules can sorb the more-toxic metal cations from the treated aqueous solution, while leaving a substantial portion of the less-toxic metal contaminant cations in the aqueous solution.
 23. A sorption medium for use in the treatment of aqueous solutions comprising at least one more-toxic metal and at least one less-toxic metal to remove at least one type of aqueous contaminant therein, comprising thermally-activated, chemically-treated granules of partially decomposed organic matter containing a synergistic interactive agent and having a Ball-Pan Hardness number of about 75-90%, and active sites on the granules occupied by cations provided by a soluble salt compound having a cation constituent and an anion constituent where: (i) the cation constituent of the salt solution is selected from the group consisting of any 1⁺ or 2⁺ cation of, without limitation ammonium (NH₄ ⁺), ammonium groups (NR₄ ⁺), sodium, potassium, lithium, cesium, beryllium, magnesium, calcium, barium, manganese, copper, zinc, strontium, and iron; and (ii) the anion constituent of the salt solution is selected from the group consisting of SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, NO₃ ⁻, NO₂ ⁻, PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, Cl⁻, I⁻, Br⁻, F⁻, HCOO⁻, CH₃COO⁻, C₂H₅COO⁻, C₃H₇COO⁻, C₄H₉COO⁻, ClO₄ ⁻, HCO₃ ⁻, or CO₃ ²⁻.
 24. The sorption medium of claim 23, wherein the synergistic interactive agent is calcium carbonate or another alkaline earth metal carbonate compound.
 25. The sorption medium of claim 23, wherein the synergistic interactive agent is a non-water soluble salt made out of anions of polyprotic acids selected from the group consisting of PO₄ ³⁻, HPO₄ ²⁻, H₂PO4⁻, SO₄ ²⁻, HSO₄ ⁻, C₂O₄ ²⁻ (oxalic acid), HC₂O₄ ⁻, C₆H₈O₄ ²⁻ (adipic acid), C₆H₉O₄ ⁻ (adipic acid), C₆H₄(COO)₂ ²⁻ (phthalic acid), and C₆H₄C₂O₄H⁻; and cations of an alkaline earth metal cations selected from the group consisting of Ca²⁺, Mg²⁺, Be²⁺, Ba²⁺, and Sr²⁺. 